[Feature Request] Implement Versioning Process to Pull Request functionality

## Feature Description
Update the Pull Request Strategy to reflect the Release Strategy which is outlined in this document:
[releases.md](https://github.com/google/stellar-engine/blob/main/releases.md)

## Use Case
Solves the issue of PRs not being tagged appropriately or confusion around the versioning process.

## Proposed Solution
Create the appropriate tags and release models so we can merge in code into appropriate stellar engine versions with a path to upgrade for appropriate customers

## Compliance & Deployment Context
* **Target Deployment Type(s):**
* [ ] US Region Restricted (e.g., Access Policy constraint)
* [ ] FedRAMP Medium
* [ ] FedRAMP High
* [ ] DoD IL4
* [ ] DoD IL5
* [x] All / General
* **Relevant NIST 800-53r5 Controls:** (If applicable, list the controls this feature helps satisfy)

## Reusability Check
Stellar Engine prioritizes reusability.
* [x] I have checked if this functionality can be achieved by extending an existing module or blueprint.
* [x] I have verified that this does not duplicate existing functionality.