fix: migrate various missed code-paths to SDK v3

[mrgrain]

Changes to production code

• Migrated inventory canary function to SDK v3.
• Migrated package versions table widget function to SDK v3.
• Pulled out a new shared helper function to decompresses a possibly gzip'ed blob stream into a string. It's used in the above migrations.
• Updated imports in some lambda handlers from import * as aws to explicitly importing the used clients to make it more obvious which code has already been migrated.
• Removed some now unused SDK v2 clients from the shared client code.
• Fixed an issue in the shared s3ObjectExists helper that would only return false when the bucket is not found, but not when the key is not found.

Changes to test cases

• Cleanup of old mocks in some unit tests.
• Refactor deny-list integ test to use assertions instead of triggers. As it was, this integ test still blocked automated dependencies updates because the hash of the trigger functions would change, causing a replacement of the trigger function. This was classified as a destructive change and failed the test. With assertions, these kind of changes are excluded.

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