Update 'quarkus-oidc' and 'quarkus-oidc-client' to get secrets from CredentialsProvider

[sberyozkin]

Fixes #15125.

This PR has the following updates:

• introduces Credentials.Provider configuration group
• Both Credentials.Secret and Credentials.Jwt groups can use a client secret; so Credentials.Secret now has a provider property to specify a secret key (quarkus.oidc.credentials.client-secret.provider.key) that should be used to retrieve a secret, similarly for Jwt - but since Jwt can have not only a client secret but also a private key configured, the property is called secret-provider which one can use as quarkus.oidc.credentials.jwt.secret-provider.key
• Updated some of the existing quarkus-oidc/quarkus-oidc-client tests to use a test CredentialsProvider
• Updated OidcClient Authentication docs to refer to the new options and also added a similar section to the OIDC web-app docs since the config root is different
• Few other minor doc and code updates

[radcortez]

@radcortez Hi Roberto, can you please glance over the changes, I can not have Provider ConfigGroup initialized. I've tried many options - it is currently inside the Credentials/Secret bean, I tried to move it under Credentials and also under OidcTenantConfig. It is always empty. I'm 100% sure I'm doing something silly :-), just can't spot what :-)

Does this happen when you use a QuarkusDevModeTest?

@sberyozkin: Hi Roberto, it was happening but then after tweaking a few things in the code I made it work - it was a buggy draft PR :-), all is good in the configuration space, sorry for the noise

[quarkus-bot]

This workflow status is outdated as a new workflow run has been triggered.

🚫 This workflow run has been cancelled.

Failing Jobs - Building bd7165d

⚠️ Artifacts of the workflow run were not available thus the report misses some details.

Status	Name	Step	Test failures	Logs	Raw logs
⌛	Initial JDK 11 Build	Cache Maven Repository	⚠️ Check →	Logs	Raw logs