Customize codec for base64JSON throws runtime error

### Summary

The `id: ID!` values produced by the `NodePlugin` and the `NodeIdCodecBase64JSONPlugin` plugin are not URL-safe. This means, if I wanted to use these ID's as part of a URL, I'd have to do additional client-side logic to make them URL safe. I'd instead like to customize/override the codec to use a url-safe base64 encoding. I'm finding not able to do so successfully.

### Steps to reproduce

When creating a plugin like this:

```typescript
import "graphile-config";
import { NodePlugin } from "graphile-build";

function base64JSONEncode(value: any): string | null {
return Buffer.from(JSON.stringify(value), "utf8").toString("base64url");
}
base64JSONEncode.isSyncAndSafe = true; // Optimization
function base64JSONDecode(value: string): any {
return JSON.parse(Buffer.from(value, "base64url").toString("utf8"));
}
base64JSONDecode.isSyncAndSafe = true; // Optimization

export const NodeIdCodecBase64URLJSONPlugin: GraphileConfig.Plugin = {
name: "NodeIdCodecBase64URLJSONPlugin",
version: "1.0.0",
description: `Adds a URL-safe 'base64JSON' codec for NodeIDs`,
after: [
NodePlugin.name,
],
schema: {
hooks: {
init(_, build) {
if (!build.registerNodeIdCodec) {
return _;
}
build.registerNodeIdCodec({
name: "base64JSON",
encode: base64JSONEncode,
decode: base64JSONDecode,
});
return _;
},
},
},
};
```

...configured with a `plugins` and `presets` configuration that ignores the stock codec:
```typescript
{
extends: [
PostGraphileAmberPreset,
PostGraphileRelayPreset,
],
plugins: [
NodeIdCodecBase64URLJSONPlugin,
],
disablePlugins: [
// disable existing plugins
NodeIdCodecBase64JSONPlugin.name,
],

}
```

### Expected results

I'd expect code that currently relies on this codec to work successfully.

### Actual results

I get a runtime error thrown from inside the `PgTableNodePlugin`:

```
Error occurred during watch schema generation: Error: Could not find Node ID codec 'base64JSON'
at Object.getNodeIdCodec (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/plugins/NodePlugin.js:58:35)
at init (/workdir/node_modules/.pnpm/graphile-build-pg@5.0.0-beta.10_@dataplan+pg@0.0.1-beta.8_grafast@0.0.1-beta.8_graphile-build_u4y5pffkmjvd272uyyrjurxzfq/node_modules/graphile-build-pg/dist/plugins/PgTableNodePlugin.js:100:38)
at SchemaBuilder.applyHooks (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/SchemaBuilder.js:98:30)
at SchemaBuilder.createBuild (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/SchemaBuilder.js:148:14)
at SchemaBuilder.buildSchema (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/SchemaBuilder.js:157:28)
at buildSchema (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/index.js:322:28)
at /workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/index.js:467:56
at watch (/workdir/node_modules/.pnpm/graphile-build@5.0.0-beta.9_grafast@0.0.1-beta.8_graphile-config@0.0.1-beta.3_graphql@16.8.1/node_modules/graphile-build/dist/index.js:246:13)
```

### Possible Solution

I'd be equally happy to propose a change to the stock `NodeIdCodecBase64JSONPlugin` implementation to use the `base64url` buffer encoding as I'm doing above — but I'm unsure the extent to which this would be an undesirable or breaking change.