Added table name and styling to volunteers without supervisors table

[leevic31]

What github issue is this PR for, if any?

Resolves #6025

What changed, and why?

Added a table name to the table that shows active volunteers without supervisors. The title is Volunteers without Supervisors. Changed the styling of this table to match the other tables in the supervisors page.

Screenshots please :)

[elasticspoon]

One small comment but looks good besides that. Thank you!

[compwron]

CI says

     # --- Caused by: ---
     # Capybara::ElementNotFound:
     #   Unable to find checkbox "user_receive_sms_notifications" that is not disabled
     #   ./spec/system/users/edit_spec.rb:211:in `block (3 levels) in <top (required)>'

Finished in 6 minutes 28 seconds (files took 8.63 seconds to load)
2979 examples, 1 failure, 5 pending

Failed examples:

rspec ./spec/system/users/edit_spec.rb:199 # users/edit volunteer user displays notification events selection as disabled if sms notification preference is not selected

Unclear to me whether it's a flake or a valid failure

[elasticspoon]

Runs locally for me, I am willing to call it a flake