[dagit] Crag: solid -> op
For crag-flagged users, rename "solid" to "op". Redirect /solids URLs to /ops, relabel stuff, etc.
Also change the search dialog placeholder to reference jobs instead of pipelines, which we had overlooked.
I am guessing there are places in Dagit that I missed here, so let's keep chipping away as we find them.
Test Plan: With flag enabled, verify that I see "ops" everywhere and that redirects work. With flag disabled, verify that everything remains "solids".
Reviewers: bengotow, sandyryza
Reviewed By: sandyryza
Differential Revision: https://dagster.phacility.com/D8954