Update gitignore in root to avoid signing metadata files in downloader (#22155)

* Update gitignore in root to avoid signing metadata files in downloader

* Fix the gitignore rule

Author: AAraKKe

.gitignore

@@ -141,3 +141,8 @@ size-compressed.txt
 # Docker secrets
 .env
 treemap*.png
+
+# Ignore any metadata file except root json in the downloader
+datadog_checks_downloader/datadog_checks/downloader/data/repo/targets
+datadog_checks_downloader/datadog_checks/downloader/data/repo/metadata/*
+!datadog_checks_downloader/datadog_checks/downloader/data/repo/metadata/root.json