[APM] Break down error table api removing the sparklines

[cauemarcondes]

A pre-requisite to implement the time series comparison is to remove the sparklines from the transaction table API and calling a new API that returns it.

GET /api/apm/services/{serviceName}/error_groups

To dos:

[] Remove sparkline timeseries from API, the avg values must stay because it should be sortable on the table.
[] Remove pagination from API
[] Create a new API that returns the sparkline timeseries based on the group_id received as property

[elasticmachine]

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