[#53289573] Fix pipeline request_type bug

Existing bug which blows up in development due
to trying to call id on nil. No issues in production
as whiny nils are turned off. RequestType 4 is not
used, so there weren't even nasty side effects.
[#53289573] Start batch task starts batch (and requests)

Previously all tasks would start the batch on render.
This adds a new task type, which will allow us to
decouple the behaviour, ensuring the starting of
batches reflects the start of labwork.

This task is designed to be transparent.

Note: This commit only adds the tasks. They are
implimented in the next commit.
[#53289573] Switch to using task based starting

- Remove old batch starters
- Add task to workflows
Merge branch 'production' into 53289573_requests_should_start_when_work_commences
[#53289573] Update start events to be simpler
Merge branch '53289573_requests_should_start_when_work_commences' of github.com:JamesGlover/sequencescape into 53289573_requests_should_start_when_work_commences
Resolve merge conflict
Merge pull request #787 from JamesGlover/53289573_requests_should_start_when_work_commences

53289573 requests should start when work commences