Add a 'jobs' view that people can select from

[benjie]

Description

Adds a public graphile_worker.jobs view that can be selected from. It is not recommended to use this since it has performance overhead, but it's better to use it than to read from the underlying tables.

Performance impact

Should not have any impact unless the view is used. We recommend that you only use the view when essential, and that you don't poll it frequently.

Security impact

Since it's a view it does bypass the row-level security policies on the underlying tables, but the payload has been removed so this is unlikely to cause a significant security issue. We aren't using security barrier because this would require us to bump the minimum supported version of Postgres. We do not GRANT any access to this view, so most roles should get permission denied errors when they attempt to select from it, depending on the default privileges your database is configured with.

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.