Add `ListPullRequestCommits`

[EyalDelarea]

• [x] All tests passed. If this feature is not already covered by the tests, I added new tests.
• [x] I used go fmt ./... for formatting the code before submitting the pull request.
• [x] This feature is included on all supported VCS providers - GitHub, Bitbucket cloud, Bitbucket server, GitLab and Azure Repos.
• [x] I added the relevant documentation for the new feature.

---

// Go context
ctx := context.Background()
// Organization or username
owner := "jfrog"
// VCS repository
repository := "jfrog-cli"
// Pull Request ID
pullRequestID := 1

// List commits for a pull request
commitsInfo, err := client.ListPullRequestCommits(ctx, owner, repository, pullRequestID)

📊 Feature Matrix – ListPullRequestCommits Support

Provider	Supported	Notes
GitHub	✅	Uses official API with retry
GitLab	✅	Uses MergeRequests.GetCommits
Azure Repos	✅	Uses GetPullRequestCommits
Bitbucket Cloud	✅	Uses PullRequests.Commits
Bitbucket Server	🚧	Not supported