[APM] Break down transaction 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}/transactions/groups/overview

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 service names received as property

[elasticmachine]

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