Update RLN spec

[oskarth]

Problem

Currently RLN spec is in a generally solid state, but it is slightly out of date, which makes it less reliable to use as a source of truth for people working on or around RLN to various capacities.

Additionally, there's no (active) editor for the spec, and its status should be draft, now raw.

Acceptance criteria

Updated RLN spec with the following:

• [x] New editor (Blagoj left PSE)

• [ ] Draft mode (all implementations agree this corresponds to it; see https://rfc.vac.dev/spec/1/ for lifecycles)

• [x] Relevant semantics updates https://github.com/Rate-Limiting-Nullifier/rln_circuits/pull/2

  • [x] https://github.com/vacp2p/rfc/issues/560

• [x] Sanity check of spec that it actually corresponds to current state

• [x] Update code example to use correct library https://rfc.vac.dev/spec/32/#identity-credentials-generation

• [x] Reference that you can use Zerokit library as well

Notes

As for editor, do we have any candidates? Ideally someone from PSE, for example @AtHeartEngineer. Alternatively someone from Vac could do this too like @rymnc, but it'd probably be better with someone from PSE since RLN as a primitive is primarily developed there.

It is also OK for non-editor to do contributions obviously.