Taskcluster-taskgraph

Added
- Support for Matrix, Slack and pulse in notify transforms

Changed
- Renamed `taskgraph.transforms.release_notifications` to `taskgraph.transforms.notify`
(including backwards compatible shim)

Fixed
- `taskgraph.parameters._get_defaults` catches `mozilla_repo_urls.errors.UnsupportedPlatformError` in order not to bust `mach` commands

Fixed
- Only depend on zstandard in the 'load-image' extra to avoid large (likely unused) binaries

Added

- Ability to enable/disable the `always_target` attribute via a new `enable_always_target` parameter

Added
- `fetch-content` has improved support for git submodules
- `fetch-content` can fetch private git repositories over ssh
- `fetch-content` can optionally use chain-of-trust artifacts to validate downloads
- `fetch-content` supports repacking tar archives containing symbolic links
- `fetch-content` repacks now use the same format as the original archive
- `fetch-content` can be told to keep the `.git` directory
- `fetch-content` takes care to log git commit ids even when pointed at a branch name
- `fetch-content` uses github's archive generator to speed up cloning
- Support for the disableSeccomp capability in docker-worker v44.22.0

Fixed
- `taskgraph load-image` CLI command can now run without raising a `ModuleNotFoundError`.

Added
- Ability to override optimization strategies via parameter

Removed
- Support for pinning hg.mozilla.org fingerprint in `run-task` as it is no longer necessary

Fixed
- Use proper Treeherder route for `github-pull-request-untrusted`
- Use `parameters_loader` in `generator.load_tasks_for_kind`
- Run initial verifications after calling `register`