Feature: Add interface to declare aliases for legacy actions

[priitlatt]

At the moment there is no way to gracefully change tool namespace. For example the root namespace of app-store-connect is utterly cluttered and many of the actions could and should be grouped under relevant action groups.

For example at the moment we have action app-store-connect get-profile. But as there are a lot more profile actions, then it would make sense to create a separate action group profiles, and make the get-profile action under that as app-store-connect profiles get. Just doing a hard rename would be a breaking change that we want to avoid at all cost.

This PR adds option to add a deprecated alias via deprecated_alias parameter to @cli.action decorator. By moving forwards with the example above, with the changes from this PR we can refactor

    @cli.action('get-profile', *GetProfileArgs)
    def get_profile(...): ...

from AppStoreConnect class to ProfilesActionGroup as

@cli.action(
    'get',
    *GetProfileArgs,
    action_group=AppStoreConnectActionGroup.PROFILES,
    deprecated_alias='get-profile',
)
def get_profile(...): ...

Then both action app-store-connect get-profile and app-store-connect profiles get would do the same thing with the difference that the deprecated version does not pop up in --help messages and yields a warning message:

Using `app-store-connect get-profile` is deprecated and replaced by equivalent action `app-store-connect profiles get`.
Use `app-store-connect profiles get` instead as `app-store-connect get-profile` is subject for removal in future releases.

[artemii-yanushevskyi]

It seems like we use "legacy" and "deprecated" interchangeably, can we perhaps stick to one or the other?