MM-13893: refactor config (#10230)

* refactor utils/config* to config/

* pull validateLdapFilter into app

* clean up Config/GetConfig/GetSanitizedConfig usage

Eliminate app.GetConfig() in favour of just using app.Config() directly,
but expose app.GetSanitizedConfig() for when the old behaviour was
required.

* web: isolate config setup

* TestInvitePeopleProvider: make config explicit

* regenerateClientConfig: avoid racey map access

* integrate watch flag into app.ConfigFile option

* make app.Option return an error

* release.mk: only cp static files from config/

* release.mk: fix cp static files from config/

* api4: TestPlugin cleanup

* s/c/cfg/ for clarity

* fix merge conflict

* testlib: allow customization of testlib driver name

app/config_test.go

@@ -42,7 +42,7 @@ func TestLoadConfig(t *testing.T) {
 	appErr := a.LoadConfig(tempConfig.Name())
 	require.Nil(t, appErr)
 
-	assert.Equal(t, "http://localhost:8065", *a.GetConfig().ServiceSettings.SiteURL)
+	assert.Equal(t, "http://localhost:8065", *a.Config().ServiceSettings.SiteURL)
 }
 
 func TestConfigListener(t *testing.T) {