[Enhancement] Add start time and pause time to ccr follow info api

[yaronp68]

This is an enhancement to CCR follow info API
User story: As a user I would like to know when a replication of a leader index has started and if it is not active anymore when did it pause?

Suggested functionality
Add timestamps of follow and pause to the metadata in state and return it when user requests follower information for specific index or for all

CC: @jen-huang @martijnvg

[elasticmachine]

Pinging @elastic/es-distributed

[elasticsearchmachine]

Pinging @elastic/es-distributed (Team:Distributed)

[kingherc]

We discussed this with @tlrx and this is related also to #37740 which explains why it is difficult to have information kept around during a pause. We believe these two issues could be handled together. If #37740 finds a way to keep the settings for info purposes, it could then be considered to add the pause timestamps to that info as well.