Issue #3622816: Follow kessai's rename of a gateway instance to a payment account

Closes [#3622816].

kessai [#3621928] (kessai!72 (merged)) renames the config entity a payment names. Three names move here:

• Url::fromRoute('entity.kessai_gateway_instance.collection') -> entity.kessai_payment_account.collection, in BookingPaymentActionBase::buildConfigurationForm(). This is the one that breaks something: Url::fromRoute() raises RouteNotFoundException for a route that does not exist, so once kessai lands, the configuration form of every booking payment action fails to render rather than showing a dead link.
• Drupal\kessai\GatewayInstanceInterface -> Drupal\kessai\PaymentAccountInterface, and the kessai_gateway_instance storage id -> kessai_payment_account, both in PaymentGatewayResolverTest. A stale type there errors rather than fails, which says nothing about the resolver.

Also corrected the comment above the narrowing, which claimed yoyaku maps none of kessai's entity types for phpstan; it maps the four payment types, just not the accounts.

Nothing else moves: the resolver already asks PaymentClientInterface::isGatewayAvailable(), which kessai keeps, and yoyaku_payment.settings:default_gateway still holds an account id.

Ordering

kessai!72 (merged) has to merge first, and packages.drupal.org has to repackage 1.x-dev, or the job here resolves a kessai without PaymentAccountInterface. Draft until then.

Gate

phpcs (Drupal,DrupalPractice, CI's extension list), 1278 files, 0 errors 0 warnings. cspell against CI's config, clean on both changed files. phpstan level 5 against the docroot's current kessai reports exactly two errors, both Class Drupal\kessai\PaymentAccountInterface not found; re-run with the kessai branch on scanDirectories it is [OK] No errors, so those two are the ordering above and nothing else.