[APM] Migrate /test/apm_api_integration/tests/fleet/ to be deployment-agnostic API tests

[rmyz]

API	ESS	Serverless	Test files
PUT /api/apm/settings/agent-configuration	✅	❌	ESS: ./test/apm_api_integration/tests/fleet/apm_package_policy.spec.ts
GET /internal/apm/services	✅	❌	ESS: ./test/apm_api_integration/tests/fleet/input_only_package.spec.ts
GET /internal/apm/fleet/migration_check	✅	❌	ESS: ./test/apm_api_integration/tests/fleet/migration_check.spec.ts

[rmyz]

Blocked as POST /api/fleet/package_policies calls are returning the following error when running in serverless

@crespocarlos is taking a look into it.

[crespocarlos]

@rmyz let's close this ticket. Serverless provides a managed policy with apm included, which is apparently what this suite tries to do.
The endpoint should actually block this request, but it's nothing we need to handle ourselves.

[rmyz]

@rmyz let's close this ticket. Serverless provides a managed policy with apm included, which is apparently what this suite tries to do.
The endpoint should actually block this request, but it's nothing we need to handle ourselves.

Great, thanks for taking a look @crespocarlos