project: disable auto-gc for depth=1 in git config

During sync, `git checkout` can trigger fetch for missing objects in
partial clones. This internal fetch can trigger `git maintenance` or
`git gc` and cause delays during the local checkout phase. Set
maintenance.auto to false and gc.auto to 0 in during `_InitRemote` if
`depth=1` to ensure that implicit fetches spawned by git skip GC.

Bug: 379111283
Change-Id: I6b22a4867f29b6e9598746cb752820a84dc2aeb6
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/540681
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

git_config.py

@@ -222,6 +222,12 @@ class GitConfig:
             value = "true" if value else "false"
         self.SetString(name, value)
 
+    def SetInt(self, name: str, value: int) -> None:
+        """Set an integer value for a key."""
+        if value is not None:
+            value = str(value)
+        self.SetString(name, value)
+
     def GetString(self, name: str, all_keys: bool = False) -> Union[str, None]:
         """Get the first value for a key, or None if it is not defined.