Integrations.type migration: 3 - Copy PG triggers that maintain `has_external_wiki`, and drop old ones

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This issue is part of &6177 (closed). See that Epic for a broader description of the feature.

There are currently some PG triggers that maintain the projects.has_external_wiki cache in !49916 (merged).

The triggers contain WHEN clauses for when type = 'ExternalWikiService', these will need to be changed to trigger when type_new = 'Integrations::ExternalWiki' instead.

The process for this would be to drop the old triggers and recreate new triggers. This will need to be done inside a transaction. As there will be other triggers maintaining the type_new values (#333506 (closed)) the caches should continue to work as before.

(Note: A related trigger !51852 (merged) operates on the category column so does not need to be updated).