feat: add an option to skip building of wheel if it is exists on the wheel server

[shubhbapna]

fixes #235

It should be easy to toggle this option even via env variable by setting FROMAGER_BUILD_SEQUENCE_SKIP_EXISTING=true (see https://click.palletsprojects.com/en/8.1.x/options/#values-from-environment-variables:~:text=When%20using%20auto_envvar_prefix,is%20WEB_RUN_SERVER_HOST.)

I also moved start_wheel_server outside of the loop to avoid applying the update_wheel_mirror method twice per package

[Gregory-Pereira]

Looks good, but going to leave formal approval to the experts
/lgtm

[shubhbapna]

As discussed, i have renamed the option to match what twine uses: https://twine.readthedocs.io/en/latest/#twine-upload

Also made the resolve_wheel function public

[dhellmann]

One small change