[Prometheus integration] Refactor OOTB dashboard

[tetianakravchenko]

Prometheus integration datasets are highly customisable - so ootb dashboard might not work:

1. Evaluate if it is possible to provide generic dashboard: number of scrapes/etc
2. Does it make sense to keep existing dashboard
3. If yes - fix it to use prometheus.* metrics (x-pack add metrics under prometheus.*) instead of prometheus.metrics.*

[tetianakravchenko]

see this pr for context - #3891:

• dynamic_templates should be added for remote_write data_stream (histogram fields)
• check if dynamic_templates should be added for other fields, like prometheus.*.value, etc. current mapping:

[tetianakravchenko]

the comment above can be ignored: it was already reverted - #4060, as the initial issue - elastic/kibana#129344 was fixed