[Feature] Label History Model

### Is there an existing feature request for this?

- [X] I have searched the existing issues

### Describe the Feature

We use GitHub Labels to mark important milestones, and folks want to be able to quickly look up:

1. When labels were applied to PR's
2. How long PR's spent with a Label before the next was applied

### Describe alternatives you've considered

I've built out this type of model for Jira Issue Time in Status before, so my current plan is to just re-do that with PR/Issue Labels.

### Are you interested in contributing this feature?

- [ ] Yes.
- [X] Yes, but I will need assistance and will schedule time during your [office hours](https://calendly.com/fivetran-solutions-team/fivetran-solutions-team-office-hours) for guidance.
- [ ] No.

### Anything else?

_No response_

Use the existing Jira Issue Time in Status model as the starting reference, since the issue proposes reusing that approach for pull request and issue labels. Confirm the finished model can report when labels were applied and how long each PR spent with a label before the next one; no files or tests are named, so maintainer guidance is needed.

Written by the indexing model from the issue text.