ESQL Partial Plan Matchers

[not-napoleon]

Working towards making more lenient plan matchers to help make the tests more readable. This mostly takes the work from @alex-spies earlier PR and wraps it in the Hamcrest matcher framework. I created two matchers, one which follows Alex's original design (top down with ignorable sections), and one which looks for matching sub plans.

Still to do:

• The match function has a bunch of asserts in it, which is not the way matchers are meant to work.
• I need to wire up useful descriptions
• Correctly setting up the internals of various nodes (e.g. sending the correct Attributes) is somewhat tricky. Better mocking would help here.
• Need to try building out some more complex trees and see what additional mocking that will require