22052: Exclude container_image from container request trigram index

22052: Exclude container_image from container request trigram index

For the same reason we exclude portable_data_hash elsewhere.

Because the previous migration has not been part of any release, this
works by splitting out the container_request trigram index update to a
new migration. This way developers who ran the previous migration will
still get the update, and users will not run the rebuild the index twice
when they upgrade to Arvados 3.0.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>