add WIS 2.0 architecture details to docs

[tomkralidis]

Expand documentation with further details on WIS 2.0/architecture.

Existing pages/locations:

• https://wis2box.readthedocs.io/en/latest/wis2.html (rST source)
• https://wis2box.readthedocs.io/en/latest/how-wis2box-works.html (rST source)

[tomkralidis]

• Short description of architecture
• tropic structure/hierarchy (integrate from wmo-im/wis2-topic-hierarchy)
• notification message structure (integrate from wmo-im/wis2-notification-message)
• discovery metadata (from wmo-im/wcmp2)

We should integrate these (InterSphinx?) with the above.

[tomkralidis]

Update: initial draft being reviewed.

[tomkralidis]

Document will be ready for mid-September. TBD whether to provide inline or by reference.

[tomkralidis]

Bumping to sprint-007 as WIS 2.0 documentation evolves.

[tomkralidis]

• WIS2 architecture docs evolve pilot phase
• draft of guide for INFCOM 3 (2024)
• provide links to authoritative docs (manual/guide) from wis2box docs