NeoForge outage should not prevent container starting up

### Describe the problem

Neoforge currently has an outage which is preventing minecraft-server from starting. This is for an existing container that has been running fine until it decided to do a version check on an already installed server.

### Container definition

services:
mc:
container_name: moPack
image: itzg/minecraft-server:latest
tty: true
stdin_open: true
ports:
- "25565:25565"
environment:
EULA: "TRUE"
TYPE: "NEOFORGE"
VERSION: "1.21.1"
NEOFORGE_VERSION: "21.1.169"
MEMORY: "16384M"
MAX_PLAYERS: "5"
USE_AIKAR_FLAGS: "true"
TZ: "Pacific/Auckland"
volumes:
- "./.:/data"

### Container logs

[init] Running as uid=1000 gid=1000 with /data as 'drwxrwxrwx 1 1000 1000 4096 May 11 08:13 /data'
[init] Resolving type given NEOFORGE
[mc-image-helper] 13:39:09.709 ERROR : 'install-neoforge' command failed. Version is 1.41.5
me.itzg.helpers.http.FailedRequestException: HTTP request of https://maven.neoforged.net/releases/net/neoforged/neoforge/maven-metadata.xml failed with 502 Bad Gateway: Fetching object content
at me.itzg.helpers.http.FetchBuilderBase.lambda$failedRequestMono$2(FetchBuilderBase.java:220)
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
*__checkpoint ⇢ fetching metadata for net.neoforged:neoforge
Original Stack Trace:
at me.itzg.helpers.http.FetchBuilderBase.lambda$failedRequestMono$2(FetchBuilderBase.java:220)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:132)
at reactor.core.publisher.FluxDefaultIfEmpty$DefaultIfEmptySubscriber.onNext(FluxDefaultIfEmpty.java:122)
at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:129)
at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:224)
at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:113)
at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:194)
at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
at reactor.core.publisher.Operators$BaseFluxToMonoOperator.completePossiblyEmpty(Operators.java:2097)
at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onComplete(MonoCollectList.java:118)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260)
at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144)
at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:413)
at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:455)
at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:509)
at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:824)
at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:115)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:289)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318)
at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1519)
at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1377)
at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1428)
at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:530)
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:469)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868)
at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799)
at io.netty.channel.epoll.AbstractEpollChannel$AbstractEpollUnsafe$1.run(AbstractEpollChannel.java:425)
at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:405)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Unknown Source)
Suppressed: java.lang.Exception: #block terminated with an error
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
at reactor.core.publisher.Mono.block(Mono.java:1779)
at me.itzg.helpers.forge.NeoForgeInstallerResolver.resolve(NeoForgeInstallerResolver.java:89)
at me.itzg.helpers.forge.ForgeInstaller.install(ForgeInstaller.java:54)
at me.itzg.helpers.forge.InstallNeoForgeCommand.call(InstallNeoForgeCommand.java:87)
at me.itzg.helpers.forge.InstallNeoForgeCommand.call(InstallNeoForgeCommand.java:19)
at picocli.CommandLine.executeUserObject(CommandLine.java:2045)
at picocli.CommandLine.access$1500(CommandLine.java:148)
at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2465)
at picocli.CommandLine$RunLast.handle(CommandLine.java:2457)
at picocli.CommandLine$RunLast.handle(CommandLine.java:2419)
at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2277)
at picocli.CommandLine$RunLast.execute(CommandLine.java:2421)
at picocli.CommandLine.execute(CommandLine.java:2174)
at me.itzg.helpers.McImageHelper.main(McImageHelper.java:178)
[init] [ERROR] Failed to install NeoForge

Start at the install-neoforge command and the NeoForgeInstallerResolver, ForgeInstaller, and InstallNeoForgeCommand entry points named in the stack trace. Check how an existing server is handled when fetching NeoForge metadata returns a 502; done should be that the container starts with the already installed server despite the outage.

Written by the indexing model from the issue text.