chore!: ensure consistent secret token generation and hashing (#20388)

This PR uses the same sha256 hashing technique as we use for APIKeys. So
now all randomly generated secrets will be hashed with sha256 for
consistency.

This is a breaking change for the oauth tokens. Since oauth is only
allowed for dev builds and experimental, this is ok.

coderd/database/migrations/000388_oauth_app_byte_reg_access_token.down.sql

@@ -0,0 +1,4 @@
+ALTER TABLE oauth2_provider_apps
+	ALTER COLUMN registration_access_token
+		SET DATA TYPE text
+		USING encode(registration_access_token, 'escape');

coderd/database/migrations/000388_oauth_app_byte_reg_access_token.up.sql

@@ -0,0 +1,4 @@
+ALTER TABLE oauth2_provider_apps
+	ALTER COLUMN registration_access_token
+		SET DATA TYPE bytea
+		USING decode(registration_access_token, 'escape');