Fix OIDC/GraphQL client initialization

[jmartisk]

• make sure GraphQL client config is enhanced with OIDC stuff AFTER we're sure that the GraphQL client configs already exist
• get rid of config merger bean (it's not necessary to keep it as a CDI bean when its only purpose is to do one thing at boot)

This "should" fix intermittent failures of GraphQLClientUsingOidcClientTest, I hope...

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[quarkus-bot]

✔️ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

[sberyozkin]

Tests are green, hopefully it well help to stabilize 👍