Action regen tooling

[kariharju]

Description

Added tooling and guide for actions manifest regeneration.

How can (was) this tested?

Ran the email-sending package fix with these.

Screenshots (if needed)

Checklist:

• I have bumped the version number for the Action Package / Agent
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation - README.md file
• I have updated the CHANGELOG.md file in correspondence with my changes
• I have added tests that prove my fix is effective or that my feature works
• OAuth2: I have made sure that action has necessary scopes (works in whitelisted mode)