Migration bundles directly to a docker container

Hi guys,
we are using initcontainers in kubernetes (on prem and on aks). Every team has to create pretty long dockerfiles to generate a migration bundle and let it end in a specific target.
This is not too easy for every developer

# Problem

- Executing bundles as initcontainer requires quite a lot of steps, which are not obvious for many developers.
- The dockerfile needs one or two extra stages
- The docker build needs a target parameter to get just the initcontainer
- Write a little initscript to use env variables in the entrypoint to set the connectionstring

e.g.
```Dockerfile
ARG VERSION=0.1.0
FROM mcr.microsoft.com/dotnet/aspnet:7.0 AS base
WORKDIR /app
EXPOSE 8080
ENV ASPNETCORE_URLS=http://+:8080
COPY SSL/some_company_root.crt /usr/local/share/ca-certificates
RUN update-ca-certificates
# Creates a non-root user with an explicit UID and adds permission to access the /app folder
# For more info, please refer to https://aka.ms/vscode-docker-dotnet-configure-containers
RUN adduser -u 5678 --disabled-password --gecos "" appuser && chown -R appuser /app
USER appuser

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build
ARG VERSION
ARG configuration=Release
WORKDIR /src
COPY ["src/AksPoc/AksPoc.csproj", "src/AksPoc/"]
RUN dotnet restore "src/AksPoc/AksPoc.csproj"
COPY . .
WORKDIR "/src/src/AksPoc"
RUN dotnet build "AksPoc.csproj" -c $configuration -o /app/build -p:Version=${VERSION}

# Build the migrationbundle here
FROM build as migrationbuilder
ENV PATH $PATH:/root/.dotnet/tools
RUN dotnet tool install --global dotnet-ef
RUN mkdir /migrations
RUN dotnet ef migrations bundle --self-contained -r linux-x64 -o /migrations/migration
RUN cp ./initentrypoint.sh /migrations/initentrypoint.sh

# Stage to execute the migrationbundle
FROM mcr.microsoft.com/dotnet/aspnet:7.0 as initcontainer
ENV CONNECTIONSTRING="User Id=AZUREPOC;Password=start123;Data Source=db:1521/FREEPDB1;"
COPY --from=migrationbuilder /migrations /migrations
COPY --from=migrationbuilder /src/src/AksPoc/appsettings.json /migrations/appsettings.json
RUN chmod 755 /migrations/migration
RUN chmod 755 /migrations/initentrypoint.sh
WORKDIR /migrations
ENTRYPOINT [ "./initentrypoint.sh" ]

FROM build AS publish
ARG configuration=Release
RUN dotnet publish "AksPoc.csproj" -c $configuration -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "AksPoc.dll"]
```

Initscript:
```Bash
#!/bin/bash
./migration --connection "$CONNECTIONSTRING"
```

# Suggestion
As you see this is quite complex.
Because of that I'd love to have a command, which build a complete dockercontainer with just one command like:
```bash
dotnet efbundle --container --tag initcontainer:latest
```
This command should do all the efbundling and copying of appsettings.json into a docker container. That container should be configurable via environment variables like CONNECTIONSTRING.

Thanks in advance,
Bjego