Use git.HOME_PATH for Git HOME directory (go-gitea#20114)

* Add git.HOME_PATH

* add legacy file check

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* pass env GNUPGHOME to git command, move the existing .gitconfig to new home, make the fix for 1.17rc more clear.

* set git.HOME_PATH for docker images to default HOME

* Revert "set git.HOME_PATH for docker images to default HOME"

This reverts commit f120101.

* force Gitea to use a stable GNUPGHOME directory

* extra check to ensure only process dir or symlink for legacy files

* refactor variable name

* The legacy dir check (for 1.17-rc1) could be removed with 1.18 release, since users should have upgraded from 1.17-rc to 1.17-stable

* Update modules/git/git.go

Co-authored-by: Steven Kriegler <61625851+justusbunsi@users.noreply.github.com>

* remove initFixGitHome117rc

* Update git.go

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Steven Kriegler <61625851+justusbunsi@users.noreply.github.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/git/git.go

@@ -20,7 +20,6 @@ import (
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
-
 	"github.com/hashicorp/go-version"
 )