🌅 add fetch_repo subcommand (based on fetchsrclibs plugin)

We've been using fetchsrclibs plugin for downloading source-code for
apps and srclibs. This change copies to plugin script into fdroidserver
as a subcommand. It also renames it from fetchsrclibs to fetch_repo
because it's fetching the git repo in Repo:

fdroidserver/__main__.py

@@ -69,6 +69,7 @@ COMMANDS_INTERNAL = [
     "destroy",
     "exec",
     "execute_sudo",
+    "fetch_repo",
     "install_ndk",
     "make_source_tarball",
     "prepare_source",

fdroidserver/fetch_repo.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+#
+# fetch_repo.py - part of the F-Droid server tools
+# Copyright (C) 2024-2025, Michael Pöhn <michael@poehn.at>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Subcommand for fetching Repo: to set up source code to build."""
+
+import argparse
+import logging
+import sys
+import traceback
+
+from fdroidserver import common, metadata
+
+
+def fetch_repo_wrapper(app, build):
+    vcs, _ignored = common.setup_vcs(app)
+    vcs.gotorevision(build.commit, refresh=True)
+    if build.submodules:  # TODO move to separate subcommand: fetch_submodules
+        vcs.initsubmodules()
+    else:
+        vcs.deinitsubmodules()
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    common.setup_global_opts(parser)
+    parser.add_argument(
+        "APPID:VERCODE",
+        help="Application ID with Version Code in the form APPID:VERCODE",
+    )
+    options = common.parse_args(parser)
+    common.set_console_logging(options.verbose)
+
+    try:
+        appid, vercode = common.split_pkg_arg(options.__dict__['APPID:VERCODE'])
+        app, build = metadata.get_single_build(appid, vercode)
+        fetch_repo_wrapper(app, build)
+    except Exception as e:
+        if options.verbose:
+            logging.error(traceback.format_exc())
+        else:
+            logging.error(e)
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()