Add oauth2 client-credentials example (#1044)

Add oauth2 client-credentials example (#1044)

* Add oauth2 client-credentials example

Add an example for oauth2 config with client-credentials, valid status response codes, token url, etc.

Signed-off-by: javivaz <javier.vazquez.romera@gmail.com>
* Remove commented config

Signed-off-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>
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Signed-off-by: javivaz <javier.vazquez.romera@gmail.com>
Signed-off-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>
Co-authored-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>