Add "Breaking Release Checklist" to internal docs (#6980)

## Description

This PR adds the first version of the "Breaking Release Checklist"
document to the compiler's internal documentation.

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

docs/breaking-release-checklist.md

@@ -0,0 +1,10 @@
+# Breaking Release Checklist
+
+- [ ] Ensure that the `forc migrate` tool **in the latest patch release before the breaking change release** contains all migration steps.
+- [ ] Promote experimental features to standard features:
+  - [ ] Remove feature flags and all conditional code from the compiler.
+  - [ ] Remove experimental `cfg` attributes from all the Sway codebase in the `sway` repository. (E.g., `std` library, E2E tests, in-language tests, etc.)
+  - [ ] Remove testing experimental features from E2E tests by deleting all the `test.<feature>.toml` files.
+  - [ ] Remove testing experimental features from `ci.yml`.
+  - [ ] Close the GitHub tracking issues.
+- [ ] In the breaking change release, unregister all the migration steps in the `forc migrate`. (Do not delete the migrations. We want to keep them as examples for similar future migrations and for learning purposes.)