Added JWT example to OIDC for Services (#8915)

[paulkmoore]

Fixes #8915

[sberyozkin]

Hi @paulkmoore This reads very well, thanks, the only thing I'd like to ask for is to remove a link to JsonWebToken and refer to it either simply as JsonWebToken (package name is in the code fragment) or as org.eclipse.microprofile.jwt.JsonWebToken.
The master version, though not in the short term, may be different to what is offered in a current version of Quarkus. we can link to MP JWT 1.1.1 tag but then we'll likely forget to update the link once we move to MP JWT 2.0 for example :-)

[sberyozkin]

Hi @paulkmoore Nearly ready to go, please squash.

[paulkmoore]

Hi @sberyozkin Should be ready to go :)