Update CF connector to implement new Connector interface

[IvanChalukov]

Overview

related concourse/concourse#9577
Update callback connector API and CF implementation.

• CallbackConnector now carries connector state:
  • LoginURL(... ) returns (string, []byte, error)
  • HandleCallback(..., connData []byte, ...) accepts connector data
• Cloud Foundry connector updated to match new signatures
• CF Open() fixes:
  • check UAA well-known status via uaaResp.StatusCode
  • return error on Cloud Controller info JSON decode failure
• Added test for non-200 UAA well-known response
• Need to fully validate it on one of CF environments

Special notes for your reviewer

Validation: go test ./connector/cloudfoundry

[Kump3r]

Validated by building Concourse with:

replace github.com/concourse/dex => github.com/IvanChalukov/dex v0.0.0-20260518155201-990c8426ee83

then I replaced the binary on our Concourse bosh web instance and stopped the HA web instance to test cloudfoundry auth trough the modified binary instance. Thanks for the fix.

[taylorsilva]

note to future self: we should do these PR's directly into the relevant pr/* branch. merging directly into master will result in us losing the commits from the PR.

I'm now cherry-picking the commits over to the relevant pr/* branch.

[IvanChalukov]

Sorry for the double work @taylorsilva, I did not know that specification. I will keep that in mind next time.