feat(rln-relay): 0.15.0 release

[rymnc]

Problem

This is to keep track of the rln-relay features to be ready for integration in the next nwaku release 0.15.0.

• Refactoring to improve rln-relay interface (@rymnc)
  • feat(rln-relay): group management interface #1370
    • feat(rln-relay): abstract group management into its own api #1465

There are a couple of other low-hanging fruits which we can attempt in case the above list is completed earlier than the deadline.

Acceptance criteria

Getting the listed features ready and tested by the indicated deadline below.
Making sure there is no regression regarding the added features on the waku v2 fleets.

Deadline

February 8, 2023 (one week prior to the next release date)

cc: @jm-clius @s1fr0

[rymnc]

@s1fr0, I've moved a few issues from this release to the next to account for changed priorities re:scaling, If you feel we need to move some back please feel free to do so

[jm-clius]

Closing issue as milestone has been reached. @rymnc feel free to reopen and assign to a next milestone if necessary.