transitioner might want "acquisition" component

Very often the observer may want some slack in the transition between observing blocks, above those required to reconfigure the instrument etc. Examples include time to tweak the pointing of the telescope or to make sure a star is on the slit. This would be required to be added regardless of instrument configuration.

At the moment I am putting an ```acquisition``` key into the instrument configuration for each block, set to the target name. This works, but feels like a kludge.

Start by reading the transitioner and how it currently consumes instrument configuration between observing blocks. Clarify the proposed acquisition component's API and how it should provide slack independently of instrument configuration, using the existing target-name workaround as the behavioral reference. Done should include a defined transition behavior that supports telescope pointing or slit-check time without per-block instrument settings.

Written by the indexing model from the issue text.