Introduce release tags for actions and utilize immutable tags

We have multiple actions defined in this repository, but do not use tagged releases. This means any use of these actions must use either a hash-ref (which tools like renovate will attempt to update every time any change to the repository is made, and/or simply may not be updated in general) or point to main, which is rightfully considered poor practice.

We should:
* introduce release tags for this repository
* ensure we enable immutable releases, to reduce the impact should it be targeted as part of a supply chain attack