Register config fields without enumerating forms

[jhhazelaar]

Problem

With statamic/eloquent-driver installed, bootAddon() queried the database via Form::all() on every application boot. When that database is unreachable or not yet migrated, the whole application fails to boot — which breaks package:discover, Larastan/PHPStan analysis in CI, and first deploys.

Seen in campus-coalitie CI (phpstan job): MR 405 pipeline

Error: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'database.forms' doesn't exist
#13 vendor/concept7/statamic-mailerlite/src/StatamicMailerLiteServiceProvider.php(31)

Fix

Follows the same pattern as statamic-rad-pack/mailchimp:

• The MailerLite section is registered once with the '*' wildcard (supported by FormRepository::extraConfigFor()), so boot no longer touches the forms repository at all — no database access, and one query per request less.
• The per-form options for the mapping grid's Form field select move to a new mailer_lite_form_fields fieldtype. Its preload() resolves the form from the CP route while the configure page renders and feeds the blueprint fields to a searchable Combobox via meta. Unlike the rad-pack version this needs no extra CP route/XHR and no client-side URL parsing.
• Stored value shape is unchanged (plain field handle string), so existing form config keeps working.

Includes regression tests: boot never calls Form::all(), wildcard section registration, and fieldtype option preloading.