GC: Tombstone for attachment blob

[agarwal-navin]

Added GC tombstone feature to attachment blobs. Attachment blobs that have been unreferenced for a sufficient amount of time (sweep timeout) become sweep ready, i.e., they can be deleted by GC. With tombstone, these blobs are not deleted but marked as tombstones. Tombstone blobs cannot be retrieved but they are still present and can be recovered.

Some key changes in this PR:

• BlobManager maintains a list of tombstone blobs. Whenever a blob becomes sweep ready, it is marked as tombstone.
• In BlobManager::getBlob(), if the blob retrieved is a tombstone, an error is thrown if throwOnTombstone setting is enabled.
• Moved GC attachment blob tests from test/test-end-to-end-tests/blobs.spec.ts to test/test-end-to-end-tests/gc/gcAttachmentBlobs.spec.ts.
• Added a bunch of attachement blob tombstone tests.

Note - This is created in favor of #12880.

AB#2132

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +1.04 KB

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	410.57 KB	411.09 KB	⯅ +531 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	208.02 KB	208.54 KB	⯅ +530 Bytes
loader.js	154.98 KB	154.98 KB	■ No change
map.js	42.68 KB	42.68 KB	■ No change
matrix.js	133.32 KB	133.32 KB	■ No change
odspDriver.js	120.11 KB	120.11 KB	■ No change
odspPrefetchSnapshot.js	41.2 KB	41.2 KB	■ No change
sharedString.js	152.98 KB	152.98 KB	■ No change
Total Size	1.3 MB	1.3 MB	⯅ +1.04 KB

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Baseline commit: d43b6dc

Generated by 🚫 dangerJS against 1b94256

[tyler-cai-microsoft]

LGTM I had a few questions, but they were minor.

[tyler-cai-microsoft]

#13266 (comment)
This brings a smile to my face :)