Add OAuth2.0 support to Metrics API scaler

[edwin-Marrima]

Proposal

Metrics API scaler supports Bearer authMode, however It is necessary to pass a static token, which is not ideal for current scenarios. Firstly, it represents a security risk; and secondly, it requires the token to be changed when the encryption key is updated, which involves a significant amount of work and presents other challenges.
I suggest adding support for the OAuth2.0 client credentials flow. This way, the Metric API scaler will be responsible for interacting with the IDP to obtain tokens.

Use-Case

No response

Is this a feature you are interested in implementing yourself?

Yes

Anything else?

No response