add some example plugins for repo key extraction and migration

examples/fdroid_extract_repo_pubkey.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+#
+# an fdroid plugin print the repo_pubkey from a repo's keystore
+#
+
+from argparse import ArgumentParser
+from fdroidserver import common, index
+
+fdroid_summary = 'export the keystore in standard PEM format'
+
+
+def main():
+    parser = ArgumentParser()
+    common.setup_global_opts(parser)
+    options = parser.parse_args()
+    common.config = common.read_config(options)
+    pubkey, repo_pubkey_fingerprint = index.extract_pubkey()
+    print('repo_pubkey = "%s"' % pubkey.decode())
+
+
+if __name__ == "__main__":
+    main()