RFC 1001: Update vs upgrade

There are two concerns that RFC 1001 covers:

1. The process of updating the installed server packages, which is done via `edgedb server install --update` in the current version of the RFC.

2. The process of *upgrading* an EdgeDB server instance (i.e a data directory) to a new (major) EdgeDB version, which is done via `edgedb server upgrade` in the current version of the RFC.

@ambv pointed out that a lot of the options in `edgedb server install` do not actually apply to the `--update` mode (e. g. you cannot do `--docker --update` if the initial `install` was ran without `--docker`). Hence, the suggestion to have a separate command for installed package updates: `edgedb server update`. That, however, is very close to `edgedb server upgrade` and would be an endless source of confusion. Another idea from @vpetrovykh is to name the package update command as `edgedb server patch`.

Also, worth noting that `edgedb server install --update` is intended to update the installed package to the most recent *minor* version for a given major version.

Open questions:

1. Should update be a standalone command or part of `install`?
2. If standalone, what is the best name?
3. What is the exact interaction of `server upgrade` with `install` and `update`?