[Change] Add description of HA to Timescale Cloud/Forge

[mfreed]

We should add a section to both Timescale Cloud and Forge describing support for HA (on Cloud -> Pro Plans; on Forge -> all services are HA using disaggregated storage and automated recovery).

Additionally, we should document that both take continuous incremental backups and supported automated recovery from backups as secondary safety mechanism.

https://docs.timescale.com/latest/getting-started/exploring-cloud https://docs.timescale.com/latest/getting-started/exploring-forge