feat: Update response_types_supported to allow multiple-valued response type combinations

[Cedric-Magnan]

Overview

DEX can support multiple-valued response type combinations (spec) but doesn't display it on the server endpoint :
https://<idp_url>/.well-known/openid-configuration

This PR fixes this issue.

What this PR does / why we need it

Some applications will check the response_types_supported retrieved from the following URL : https://<idp_url>/.well-known/openid-configuration before performing any flow.

DEX servers will only display the following supported response types :

"response_types_supported": [
  "code",
  "id_token",
  "token"
]

Since DEX can support multiple-valued response type combinations, this field should display :

"response_types_supported": [
  "code",
  "id_token",
  "token",
  "code token",
  "code id_token",
  "token id_token",
  "code token id_token"
]

Closes #1449

Special notes for your reviewer

Does this PR introduce a user-facing change?

NONE

[nabokihms]

@Cedric-Magnan, hello, and thank you for opening this PR. It is a long-term issue, and we'd like to fix this!
Reviewing this PR is on my list (I hope I will get to it soon).

[sagikazarmark]

@Cedric-Magnan apologies for the delay on reviewing this PR. Would you mind rebasing it though before we proceed? Thanks!

[Cedric-Magnan]

@Cedric-Magnan apologies for the delay on reviewing this PR. Would you mind rebasing it though before we proceed? Thanks!

No problem @sagikazarmark, I've now rebased my fork from the latest commits on master

[sagikazarmark]

Looks good to me, but CI isn't running for some reason. Can you do one more rebase please @Cedric-Magnan ? Thanks!

[Cedric-Magnan]

Looks good to me, but CI isn't running for some reason. Can you do one more rebase please @Cedric-Magnan ? Thanks!

@sagikazarmark, I've rebased with the latest commit from master, the workflows can now be approved !

[sagikazarmark]

Thanks!