Add Bearer Auth for Metrics API scaler

[JorTurFer]

Adds an authorization method named bearer for Metrics API scaler

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• Tests have been added
• A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (repo) (if applicable) Add documetation about Bearer Auth for Metrics API scaler keda-docs#513
• Changelog has been updated

Relates to #1081

[JorTurFer]

I'm not sure if it's better to create a new AuthType or reuse the existing BearerAuthType

Maybe bearer is a specific case of jwt but ... 🤔
any opinion @zroubalik @ahmelsayed ?

[ahmelsayed]

JWT would be a specific case, or format, of a bearer token, right? I'm assuming the value of jwtToken is expected to be Bearer <jwt> in this case, correct?

[tomkerkhove]

JWT would be a specific case, or format, of a bearer token, right? I'm assuming the value of jwtToken is expected to be Bearer <jwt> in this case, correct?

I'd say that the JWT would just be the JWT token and we add the bearer for you, no?

[JorTurFer]

I'm not an expert here, but I think that JWT is more like the format and Bearer is one use case of the format, but as I said, I'm not an expert :(
I will try to get some help from an expert

[tomkerkhove]

I'd say that the JWT would just be the JWT token and we add the bearer for you, no?

This remark is purely from a user-perspective and making it simple/straight-forward - Not saying this is how JWT works

[JorTurFer]

Maybe the auth method should be named as Bearer instead JWT, we can simplify the process to the final user just placing the token, and we automatically add the Authorization header with the value Bearer {given token}
This could be clearer than naming it JWT auth for a Bearer auth.
WDTY?

[zroubalik]

Maybe the auth method should be named as Bearer instead JWT, we can simplify the process to the final user just placing the token, and we automatically add the Authorization header with the value Bearer {given token}
This could be clearer than naming it JWT auth for a Bearer auth.
WDTY?

I like this approach.

[JorTurFer]

I have just changed it @zroubalik :)
I think that it's ready for review

[zroubalik]

LGTM :)

[ahmelsayed]

@JorTurFer one merge conflict in CHANGELOG.md

[JorTurFer]

@JorTurFer one merge conflict in CHANGELOG.md
Hi @ahmelsayed !
I see... I had another merge conflict in the same file with the other PR that I have and I have just fixed it. I will update this but when one of them is merged, the other will need changes again :(