Make the Git username configurable for builds from Git (spec.git.username) #6874

Description

Follow-up of #6869 / #6873, as suggested in #6873 (comment).

#6873 makes the Git username configurable for the gitops trait (gitops.username). Building an Integration from a Git repository (spec.git / kamel run --git ...) still authenticates with the hardcoded username camel-k:

• pkg/builder/git.go, cloneProject, passes DefaultGitUsername (camel-k) to CloneGitProject
• GitConfigSpec (pkg/apis/camel/v1/build_types.go) has no field to configure it

To our understanding this prevents building from a private Bitbucket Cloud repository with a repository/project/workspace access token, because Bitbucket only accepts the username x-token-auth for those tokens (see https://support.atlassian.com/bitbucket-cloud/docs/using-access-tokens/).

Proposal

For parity between the Git build feature and the gitops trait:

• add a username field to GitConfigSpec, so it is available as .spec.git.username on the Integration and propagated to the Build
• cloneProject passes Build.Git.Username, falling back to DefaultGitUsername when empty (backward compatible)
• optionally a kamel run --git-username flag
• regenerate CRDs and docs

Claude Code on behalf of Jan Bouecke