Plugins: Ignore symlinked folders when verifying plugin signature (#34434) (#35719)

* add check + test

* fix test

* add manifest

* fix linter

* add nolint

* separate err cond checks

* only collect relevant plugin files

* skip symlinks

* refactor

* add missing test files + enable scanning Chromium.app/

* remove test since case already covered

* remove unnecessary changes from before

* refactor

* remove comment

(cherry picked from commit 303352a89b)

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/plugins/manager/testdata/includes-symlinks/MANIFEST.txt

@@ -0,0 +1,31 @@
+
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA512
+
+{
+  "manifestVersion": "2.0.0",
+  "signatureType": "grafana",
+  "signedByOrg": "grafana",
+  "signedByOrgName": "Grafana Labs",
+  "plugin": "test-app",
+  "version": "1.0.0",
+  "time": 1622547655175,
+  "keyId": "7e4d0c6a708866e7",
+  "files": {
+    "symlink_to_txt": "9f32c171bf78a85d5cb77a48ab44f85578ee2942a1fc9f9ec4fde194ae4ff048",
+    "plugin.json": "c59a51bf6d7ecd7a99608ccb99353390c8b973672a938a0247164324005c0caf",
+    "dashboards/connections.json": "bea86da4be970b98dc4681802ab55cdef3441dc3eb3c654cb207948d17b25303",
+    "dashboards/extra/memory.json": "7c042464941084caa91d0a9a2f188b05315a9796308a652ccdee31ca4fbcbfee",
+    "text.txt": "9f32c171bf78a85d5cb77a48ab44f85578ee2942a1fc9f9ec4fde194ae4ff048"
+  }
+}
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+Comment: https://openpgpjs.org
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