How to set up staging envs procedures

### Contributions

We should add more context and possibly these two procedures somewhere. One exists in paragraph form on the environments page, but maybe they both should become procedures?

- [ ] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

docs.getdbt.com/docs/deploy/deploy-environments

### What part(s) of the page would you like to see updated?

From initial customer beta feedback, I think there are two legitimate patterns:
1. Production = default branch (`main`)
- point Development + Staging to `staging` branch
- point Production to `main`
- promote to Production by merging from `staging -> main`
2. Staging = default branch (`main`)
- point Development + Staging to `main` branch
- promote to Production by cutting "release" branches/tags off `main` at a regular interval (daily, weekly)
- update Production environment (via [dbt Cloud Admin API](https://docs.getdbt.com/dbt-cloud/api-v3#/operations/Update%20Environment)) to point to latest "release" branch/tag

Right now we've documented (1) here. I don't want to add too much complexity here, but we should mention that it's not the only legitimate/supported pattern.

### Additional information

https://github.com/dbt-labs/docs.getdbt.com/pull/5356#discussion_r1586609498