[APM] APM client for supertest

[sorenlouv]

Related to: #83429 (comment)

Similar to how we have a API client that type checks parameters, and adds return types to responses, we should have a client that wraps supertest.

Example:

const res = await apmSupertest({
 endpoint: 'GET /api/apm/services/opbeans-java/overview_transaction_groups',
 query: {
   start,
   end,
   uiFilters: '{}',
   size: 5,
   numBuckets: 20,
   pageIndex: 0,
   sortDirection: 'desc',
   sortField: 'impact',
 },
})

In the above case res should have the correct return type. All parameters supplied should also be type checked.

I think that would provide an awesome DX - especially when editing a test to accommodate an API change

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[sorenlouv]

This is already implement