feat: add exporter & prometheus exporter

[proost]

Description

Adding Stats exporter package and prometheus exporter

Related issue(s)

:white_check_mark: Checklist for your Pull Request

Related changes (conditional)

• Tests

  • [X] If I added new functionality, I added tests covering it.
  • [ ] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

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    • README

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  • [X] My changes doesn't break project license.

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• [X] My code complies with the styles guide.

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  If necessary both of these can be achieved even after the commits have been made/pushed using rebase and squash.

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• [X] Check target branch of PR is set correctly

[maypok86]

Wow, it looks great. I think it's better to merge it a little later, along with the update of otter to v2, along with the redesign of the api, which should no longer change at all.

[maypok86]

@proost I will try to collect the ideas in this issue. It will be very cool to know your opinion.