testing: Run a nightly Contour install CI job

[youngnick]

As the operator matures, it's important for us to be confident that Contour controller changes don't break the operator.

To this end, this issue covers:

• setting up some sort of CI job that runs on a schedule (probably daily to start with, but could be more frequent if it's not too expensive)
• the job must test that projectcontour/contour:main and projectcontour/contour-operator:main work together.
• The first phase is to test that an install ( and possibly removal) works; upgrades are left as a future exercise, although we acknowledge that a previous release -> main upgrade check will be immensely valuable.
• The exact nature of the tests are left as an exercise for the implementer; something like contour's integration tests (that actually verify at least basic Contour functionality) would be very useful as well.

[danehans]

fixed by #206.