API for git-hook environments

[jolheiser]

Similar to #9093, but more focused on the available variables.
Also related to #8935, as it may benefit from having this defined.

As mentioned in #10337 (comment), this is an issue for discussing a public API for git hook environments.

What should be available in these environments?
Should certain things only be available in certain situations?
We need to be careful not to bog down the system by loading extraneous data for the sake of a hook environment. The more expensive it is, the harder it will be to justify.

I've found a few places where environments are set:

• gitea/models/helper_environment.go

  Line 42 in 48ce135

  func FullPushingEnvironment(author, committer *User, repo *Repository, repoName string, prID int64) []string {

• gitea/cmd/serv.go

  Lines 201 to 209 in 95013fd

  	os.Setenv(models.EnvRepoIsWiki, strconv.FormatBool(results.IsWiki))
  	os.Setenv(models.EnvRepoName, results.RepoName)
  	os.Setenv(models.EnvRepoUsername, results.OwnerName)
  	os.Setenv(models.EnvPusherName, results.UserName)
  	os.Setenv(models.EnvPusherID, strconv.FormatInt(results.UserID, 10))
  	os.Setenv(models.ProtectedBranchRepoID, strconv.FormatInt(results.RepoID, 10))
  	os.Setenv(models.ProtectedBranchPRID, fmt.Sprintf("%d", 0))
  	os.Setenv(models.EnvIsDeployKey, fmt.Sprintf("%t", results.IsDeployKey))
  	os.Setenv(models.EnvKeyID, fmt.Sprintf("%d", results.KeyID))

• gitea/routers/repo/http.go

  Lines 268 to 284 in cca13ae

  	environ = []string{
  	models.EnvRepoUsername + "=" + username,
  	models.EnvRepoName + "=" + reponame,
  	models.EnvPusherName + "=" + authUser.Name,
  	models.EnvPusherID + fmt.Sprintf("=%d", authUser.ID),
  	models.EnvIsDeployKey + "=false",
  	}
  	if !authUser.KeepEmailPrivate {
  	environ = append(environ, models.EnvPusherEmail+"="+authUser.Email)
  	}
  	if isWiki {
  	environ = append(environ, models.EnvRepoIsWiki+"=true")
  	} else {
  	environ = append(environ, models.EnvRepoIsWiki+"=false")
  	}

  
  

  gitea/routers/repo/http.go

  Line 316 in cca13ae

  environ = append(environ, models.ProtectedBranchRepoID+fmt.Sprintf("=%d", repo.ID))

Ideally when implemented these would all converge for ease of maintanence, if possible.