docs: add spec for status protocol stack, deprecate waku-usage spec (#…

…105)

This adds a new raw specification covering the Status protocol stack,
including:
- common app-level features (content topics, functional scopes,
ephemerality)
- e2e reliability layer
- encryption layer (TBD)
- Waku transport layer

It deprecates/replaces the previous status waku-usage spec.

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Co-authored-by: Jimmy Debe <91767824+jimstir@users.noreply.github.com>