Create a human-readable list of Miro suppressions

[alexwlchan]

This adds an extra step to the "suppress Miro image" script:

1. Scan the DynamoDB table and find all images which have been suppressed after the initial migration
2. Create a human-readable table describing those suppressions
3. Create a PR in our private docs repo that includes that table, e.g. https://github.com/wellcomecollection/private/pull/9

For #2350