[#54279622] Add options to compress old indices

In order to save space when rotating out old indices we wanted the
option to compress them once they reach a certain age (defaults to
1 day as this should mean they get compressed as soon as rotated).

This functionality can be enabled by adding the argument --compress-old
to es-rotate, with --compress-maxage expressing the cutoff time delta
(in days) before they get compressed (default 1).

As deleting old indices and compressing them shared much code, I pulled
out the logic picking old indices before running a passed in function on
them.

Because this has added new functionality to estools I have bumped the
minor version number yielding 1.1.0.
[#55883844] Add test for rotator

Rotator was getting more complex with this added feature so I added some
tests to prove the expected behavior.
[#55883844] Match formatting in tests
Merge pull request #3 from alphagov/compress-old-rotated

Compress old rotated