[593] Edit email subscription status (support functionality)

[avinhurry]

Context

We anticipate that going forward the Support team (and ourselves) will find it useful be able to see if a candidate is unsubscribed, and perhaps also edit this on their behalf should they change their mind, or request it direct via a support query rather than using an unsubscribe link.

Changes proposed in this pull request

• Surface the candidate email subscription status on the support index page
• Add the ability to update the status by clicking the change button

Screenshot

Things to check

• If the code removes any existing feature flags, a data migration has also been added to delete the entry from the database
• This code does not rely on migrations in the same Pull Request
• If this code includes a migration adding or changing columns, it also backfills existing records for consistency
• If this code adds a column to the DB, decide whether it needs to be in analytics yml file or analytics blocklist, if included inform data insights team of the changes
• If this code adds a column that may include PII, the sanitise.sql script and 0025-protecting-personal-data-in-production-dump.md ADR have been updated
• API release notes have been updated if necessary
• If it adds a significant user-facing change, is it documented in the CHANGELOG?
• Attach the PR to the Trello card

[avinhurry]

Support Console: The ability to see and edit whether a candidate is unsubscribed from subscription emails

[dcyoung-dev]

Good work, I've left a few comments/suggestions but none of them are blockers