feat: Progressive rollouts

[jsirianni]

This PR implements support for Progressive Rollouts.

The action will check if the head commit matches the following regex:

progress rollout (\S+)$

Commit messages can look like this:

• This is a commit progress rollout my-config
• progress rollout my-config

This allows the user to include context. the progress rollout <name> piece must be at the end of the commit message.

If the head commit does not contain the progress rollout message, the normal workflow will execute.