[MM-41576] Revamp database schema version (#19586)

* revamp db version and add applied migrations endpoint

* replace old schema version with new

* add db version subcommand

* add to local api

* reflect review comments

* log errors

* remove setting the version from model.CurrentVersion

* fix a test

app/post_test.go

@@ -464,6 +464,7 @@ func TestImageProxy(t *testing.T) {
 	mockStore.On("User").Return(&mockUserStore)
 	mockStore.On("Post").Return(&mockPostStore)
 	mockStore.On("System").Return(&mockSystemStore)
+	mockStore.On("GetDBSchemaVersion").Return(1, nil)
 
 	th.App.UpdateConfig(func(cfg *model.Config) {
 		*cfg.ServiceSettings.SiteURL = "http://mymattermost.com"