feat: move termix identity into a plugin (C6)

drizzle/mysql/0055_icy_patch.sql

@@ -0,0 +1,4 @@
+-- termix_identities, termix_identity_keys and termix_identity_ca move to the
+-- termix-identity plugin's adopted tables at activation. Dropping them here
+-- would lose the data first.
+SELECT 1;