Feature request : deferred manual locking of resource by user

Users can click a button in Lockable Resources page on Jenkins to grab a resource. They can also "Unreserve+Reserve" a resource to take it away from a job that currently uses it - which can have adverse effects depending on that job's structure (e.g. calling sub-jobs using the same limited resource).

This feature proposes that there should be a way for users to request a resource (any by label, or specific by name) to be assigned to them after this resource is freed by its current consumer, as well as to cancel such pending requests.

The use-case is for example to schedule maintenance on hardware nodes of the test farm or validator postmortem investigation after failed tests (requesting a deferred lock of a specific device), or for developer use/experiments (deferred lock on any device with a label match).

Bonus points for notifications (IM, Mail) to the users when they are finally granted exclusive access to that resource - so they can begin working with it.