Improve CI persistence and MSRV testing, automate issue triage

## Overview

Improve BDK Wallet CI processes for persistence and MSRV testing, and add automated issue triage.

**Description**

This is a tracking issue to improve our automated CI (continuous integration) testing and issue triage. For the CI improvements we need GitHub actions that run on every PR to confirm that no persisted data incompatibilities were introduced. We already have Github actions that confirm the codebase compiles both on the stable rust version and our chosen MSRV (minimum supported rust version), but these tests are brittle and hard to maintain. And finally for issue triage it would be nice to have a GitHub action that helps close stale issues so project contributors have an accurate list of issues to be worked on.

**Expected Outcomes**

The issues and sub-issues below should be completed.

- #234
- Add CI process to verify data created with the prior release version can be loaded with a new version
- Add CI process to verify data created with new version can be loaded with the prior release version
- Improve MSRV testing
- #400
- #79
- https://github.com/bitcoindevkit/bdk_wallet/issues/386
- Enforce signed commits
- see: https://github.com/luisschwab/bdk-floresta/blob/master/.github/workflows/sigs.yml

**Resources**

- [Github actions](https://docs.github.com/en/actions)
- [cargo-rbmt](https://github.com/rust-bitcoin/rust-bitcoin-maintainer-tools/tree/master/cargo-rbmt)
- [stale action](https://github.com/actions/stale)

**Skills Required**

- hands on experience with git and GitHub
- basic rust programming skills
- basic sqlite DB skills
- be able to sign your git commits

**Mentor(s)**

@notmandatory

**Difficulty**

Medium

**Competency Test (optional)**

- Create a repo in your personal GitHub account
- Create and commit a simple rust "hello world" app with properly signed commits
- Add a simple Github Actions job to build and check the formatting of your app
- Add a feature branch to change your app in some way
- Create a PR from your feature branch