Drop the gokrb5 replace directive

[codebien]

The gokrb5 project is not very active. We already applied a major patch in a fork under Grafana org. As there isn't any evolution on the upstream repository, we intend to do a next step on the fork and make the "github.com/grafana/gokrb5" available as a go importable library.

It allows to drop the replacement in the go.mod file and consequentially fix the CI's step for the linter and simplify the installation/building procedures.

[joanlopez]

Action plan (27/05)

• Merge testenv pull request: Establish cross-realm trust between main and sub-domain gokrb5-test#1
• Q1: Update Docker images & references? (from jcmturner/gokrb5 to grafana/gokrb5) - I guess so
  • Open & merge a pull request to replace references in gokrb5-test
  • Q1.1: Use ghcr.io instead? - A bit less "official, probably easier"
  • Q1.2: Add a release workflow (automate it)? - Worths the effort, probably easier"
  • Open & merge a pull request to automate the publication of gokrb5-related images to ghcr.io
• Open & merge a pull request to replace references in gokrb5
• Update & merge Support for complex cross-realm scenarios gokrb5#1
• Open & merge a pull request to replace paths and go.mod (v8) in gokrb5 (to make it "importable")
• Open & merge a pull request in xk6-kerberos to:
  • Drop the replace directive
  • Update the dependency (go.mod) and imports.
• Q2: Do we want to manage versioning? - I guess not, as it's not required
• Q3: Anything else?
• Q3.1: Add a WARNING in both gokrb5 repositories?