Also:
- removed `throttle` file (throttling is not covered in `alert-anatomy` page)
- fixed ctx model parameters in templates/scripts to use the `ctx` prefix.
- added a dediated section in alert-anatomy about execution context as template/script model
- wrote first page of `transform` section
Original commit: elastic/x-pack-elasticsearch@471ca7f0d9
uboness
Martijn van Groningen