Add more in-depth documentation about clouud-enabled hubs

[bsweger]

We recently merged a hubDocs PR to include some high-level information about the recent v2.0.1 schema revision (i.e., adding the cloud section to admin.json).

While that change acknowledges the existence of cloud-enabled hubs, it's lacking some important details. Once the cloud infrastructure is further developed (perhaps once the parquet data conversion process is enabled?) we should ensure that hubDocs includes enough information for people to understand what a cloud-enabled hub offers and how it works.

For example:

• Actual contact information for people who want Hubverse hosting
• Step-by-step for cloud onboarding? (copy the GitHub action, update admin.json)
• Breakdown of what the GitHub action does (including answers to some of the good questions from a recent demo, like "what happens if there are multiple merges at the same time")
• Security note
• Documentation about any data conversions happening once hub date is in S3 (e.g., formatting as parquet)