Support jwt-bearer grant-type (RFC7523) in oatuh2 extension

[JorTurFer]

Component(s)

extension/oauth2clientauth

Is your feature request related to a problem? Please describe.

Currently, only client_credentials grant type is supported. This is useful but still limits a bit the options for modern applications which could rely on other oauth grant types

Describe the solution you'd like

extensions supports RFC7523 (JSON Web Token (JWT) Profile
for OAuth 2.0 Client Authentication and Authorization Grants)

Additional context

I'm willing to contribute with the fix. Prometheus added it some days ago too -> prometheus/common#862

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[github-actions]

Pinging code owners:

• extension/oauth2clientauth: @pavankrish123

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