enhance(api): add GitHub-compatible /repos/{owner}/{repo}/commits/{ref} endpoint (#38770)

Gitea currently exposes the endpoint:
 
`GET /repos/{owner}/{repo}/git/commits/{sha}`
 
to retrieve a single commit. However, GitHub provides the equivalent
endpoint as:
 
`GET /repos/{owner}/{repo}/commits/{ref}`
 
Applications integrating with both GitHub and Gitea must implement
platform-specific logic to use different endpoints, reducing API
compatibility.
 
Fixes #38225

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

routers/api/v1/repo/commits.go

@@ -24,7 +24,7 @@ import (
 func GetSingleCommit(ctx *context.APIContext) {
 	// swagger:operation GET /repos/{owner}/{repo}/git/commits/{sha} repository repoGetSingleCommit
 	// ---
-	// summary: Get a single commit from a repository
+	// summary: Get a single commit from a repository, it has a GitHub-compatible alias "/repos/{owner}/{repo}/commits/{ref}"
 	// produces:
 	// - application/json
 	// parameters: