Rename cml ci to follow the cml <noun> <verb> naming convention

[0x2b3bfa0]

The cml ci command hasn't been renamed as part of #1073 because we didn't agree on naming. See #1073 (comment) for more information.

[0x2b3bfa0]

As per cml.dev/doc/ref/ci this command “prepares Git repository for CML operations” and, lacking a better alternative, my first proposal would be renaming it to cml repo prepare to fit its description.

[0x2b3bfa0]

The current cml ci name was inspired by the npm ci command, which provides completely unrelated functionality.

[dacbd]

though I prefer the shorthand, this does already exist for us. Re-open if this requires more discussion.

[casperdcl]

Can we please remove the misleading deprecation warning (it recommends using cml repo prepare)?

Fine by me to do any of the following instead:

• cml ci
• cml ci setup
• cml ci <verb>

[casperdcl]

moved to #1287, fixed by #1288