rework limiting digest checking for docker hub and allow with setting

[Tom-V]

This PR adjusts the recently introduced behavior that limits digest watching.

By default, digest checks are now limited to Docker Hub. The previous behavior can be restored using the WUD_REGISTRY_HUB_PUBLIC_WATCHDIGEST environment variable. The warning shown when digest watching is disabled can be suppressed using WUD_REGISTRY_HUB_PUBLIC_SUPPRESSDIGESTWATCHWARNING.

The override is useful in scenarios such as:

• Using a paid Docker Hub account with higher rate limits
• When having a daily CRON check instead of hourly

Documentation also has been updated accordingly.

Changes

Digest checking

• Moved digest checking logic to the Docker Hub registry implementation
• Re-evaluate watchDigest when reading configuration from storage

Registry image watch detection

• Simplified the helper used to determine whether a registry is watching a given image
• The helper now only requires the image name, which simplifies typings and tests

Code improvements / cleanup

• Removed most // @ts-nocheck directives where possible
• Added missing TypeScript typings
• Replaced JSDoc type annotations with TypeScript types
• Removed ensureLogger from the Docker watcher (it was masking errors and should no longer be necessary)