[APM] Loading services when creating a new agent configuration is very slow

[sorenlouv]

When creating an agent configuration, the user can select a service in a dropdown

The dropdown can be extremely slow and sometimes timeout.

Possible solutions

One idea would be to allow users to define through a text input field. We can then async check and the user doesn't have to wait for the select to become available. Another benefit is that a user can specify a service that is not yet capturing data.

#58316
#55729

[elasticmachine]

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

[formgeist]

@sqren Updated the description with the solution written out, just need to ping PMs to see if it's something we want to prioritize.

[sorenlouv]

Thanks!