MM-18517: Plugin Marketplace (Phase 2) (#13086)

* MM-17549: use StatusNotFound when deleting plugin (#12983)

Trying to delete a plugin that does not exist should fail with a 404, not a 400.

Relates-to: https://mattermost.atlassian.net/browse/MM-17549

* MM-19630: marketplace: model ReleaseNotesURL (#13083)

Automatic Merge

* MM-20065: allow prepackaged plugin upgrade (#13076)

* MM-20065: allow prepackaged plugin upgrade

When locally installing prepackaged plugins, skip if a plugin exists with the same id and is the same or a newer version.

This is effectively a "poor man's" rework of prepackaged plugins to allow upgrade of prepackaged plugins via the marketplace. The larger plan to rework prepackaged plugins was deferred from v5.18.

Fixes: https://mattermost.atlassian.net/browse/MM-20065

* eliminate unnecessary installPlugin

* fix TestPluginSync defaults to match minio

* cleanExistingBundles

* close prepackaged filereader

* simplify

app/plugin_test.go

@@ -483,7 +483,7 @@ func TestPluginSync(t *testing.T) {
 
 				s3Port := os.Getenv("CI_MINIO_PORT")
 				if s3Port == "" {
-					s3Port = "9001"
+					s3Port = "9000"
 				}
 
 				s3Endpoint := fmt.Sprintf("%s:%s", s3Host, s3Port)