The task description now includes
* flexible specification of index routes (this will get simpler once buildbot
and gecko.v1 routes are removed)
* "run-on-projects", indicating the projects on which this task should run
* "{level}" is allowed in workerTypes
* For the docker-worker/docker-engine worker implementations, "docker-image"
can have the form {in-tree: in-tree-name} to use an in-tree image. This was
previously implemented in the test transforms, but it is useful for other
tasks too!
* Optimizations, currently limited to "only-if-files-changed", can be specified
for each task.
* TreeHerder groupSymbol is optional
* expires-after and and deadline-after have default values (with the former
differing for try and non-try)
* coalesce-name triggers creation of both a coalesce route and a superseder URL
MozReview-Commit-ID: 70vtYs5lz5P
Rename to taskgraph.transforms.task.
This also adds some Required and Optional declarations to the schema to be explicit,
and adjusts the transform to handle treeherder being optional.
MozReview-Commit-ID: FuKYayvlwB9
