[DO NOT MERGE] Rename package name to fleetdb

[Alva8756]

Hi @DoctorVin and @joelrebel ,

This PR occurs to me while I am working on creating the fleetdb images running on sandbox.

To my understanding eventually we need to make this PR to migrate package name from serverservice to fleetdb. However this involves clients(conditionorc, flasher, mctl, etc) migration from importing serverservice package to fleetdb.

I am wondering do we have a plan about the migration steps?
This PR looks like the second last steps, and the last steps will be migrating clients one by one?

[DoctorVin]

I have given this migration some thought. This is a reasonable first step (although I think I'd move a little slower in the vast renaming). Changing this code so that the go compiles and the modules are reachable is a good start, but it doesn't even have to be the first one. My first goal is getting this up and running with CrDB 23.1.11 just as a complete clone of Serverservice. Then we tackle the programming aspects of changing all the names, the modules, the packages and images. Once that's deployable, we swap FleetDB for Serverservice, letting the clients all think they're connected to Serverservice. Then modify the controllers so they internally all reference FleetDB, both in code and configuration. Finally we can start making changes to the schema and API, adjusting things as we go.

[joelrebel]

Can we also lose the vanity go import path, so instead of go.hollow.sh/fleetdb its github.com/metal-toolbox/fleetdb