Regex refs for auto_deploy_on

[jerr0328]

We would like to be able to use the autodeploy feature for tags matching certain patterns. The use case is as follows:

• Dev environment will autodeploy on the main branch.
• Staging environment will autodeploy on tags with a version number and an alpha suffix (GitHub's releases would call this a "pre-release"). Example: v2a2.
• Production environment will autodeploy on tags with a version number and no suffix (e.g. v2).

One way to avoid confusion between the existing * refs and regex could be to simply use a new option, auto_deploy_on_regex where we could specify a regex, e.g. refs/tags/v\d+(a\d+)?.

Some caveats: You may want to make sure that these regex patterns must match the whole line, not just part of it, to avoid unexpected behavior. If not, it would be important to document how this config works so that the right regex is constructed.