Add test that ensures that SO types are not removed

[joshdover]

Now that migrations fail fast when a document of an unknown type is detected (#101052), we need to be sure that plugins do not inadvertently remove an SO type without either:

• Registering the SO type as deprecated (depends on [SO Migration] add an API to notify that a type is no longer used #104246); or
• Adding the type to the unusedTypesQuery:

  kibana/src/core/server/saved_objects/migrations/core/elastic_index.ts

  Lines 35 to 43 in d920682

  	export const excludeUnusedTypesQuery: estypes.QueryDslQueryContainer = {
  	bool: {
  	must_not: [
  	// https://github.com/elastic/kibana/issues/91869
  	{
  	term: {
  	type: 'fleet-agent-events',
  	},
  	},

We need to run this test against prior minor versions as well to be sure there aren't any that were removed in past versions that could create a problem.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)