Taskcluster-taskgraph

Removed

- Support for `disableSeccomp` capability. This was removed in Taskcluster 45.0.0 as it was
determined to be unnecessary.

Added

- New `rebuild_cached_tasks` action to facilitate regenerating long-lived tasks

Changed

- Updated `image_builder` Docker image to version 5.0.0

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