git-grep: set timeout to 2s by default and allow configuring it

We need to shorten the timeout to bound effectively for
computation size. This protects against "too big" repos.
This also protects to some extent against too long lines
if kept to very low values (basically so that grep cannot run out
of memory beforehand).

Docs-PR: forgejo/docs#812

modules/git/grep.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"time"
 
 	"code.gitea.io/gitea/modules/setting"
 )
@@ -94,6 +95,8 @@ func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepO
 	opts.MaxResultLimit = cmp.Or(opts.MaxResultLimit, 50)
 	stderr := bytes.Buffer{}
 	err = cmd.Run(&RunOpts{
+		Timeout: time.Duration(setting.Git.Timeout.Grep) * time.Second,
+
 		Dir:    repo.Path,
 		Stdout: stdoutWriter,
 		Stderr: &stderr,