[BRANDING] alias {FORGEJO,GITEA}_{CUSTOM,WORK_DIR}

FORGEJO_* environment variables are set to the corresponding GITEA_*
variable when the cli starts. This approach is intended to minimize
the conflicts on rebase. All occurences of GITEA_* are left untouched
in the codebase and they are only changed to FORGEJO_* if exposed to
the user.

(cherry picked from commit e466f9d10e)
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Conflicts:
	main.go
	https://codeberg.org/forgejo/forgejo/pulls/1216
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main.go

@@ -40,7 +40,16 @@ func init() {
 	setting.AppStartTime = time.Now().UTC()
 }
 
+func forgejoEnv() {
+	for _, k := range []string{"CUSTOM", "WORK_DIR"} {
+		if v, ok := os.LookupEnv("FORGEJO_" + k); ok {
+			os.Setenv("GITEA_"+k, v)
+		}
+	}
+}
+
 func main() {
+	forgejoEnv()
 	cli.OsExiter = func(code int) {
 		log.GetManager().Close()
 		os.Exit(code)