RC.5.0 Port - Put Memory Blob Storage Under a Flag (#21612)

[anthony-murphy]

We recently made changes to how detached blob storage works, and enabled a default in-memory blob storage such that blobs would be supported by default in detached containers.

However, when blobs are in a detached container, it changes the container attachment flow, specifically, an empty file is created, the blobs are uploaded, and then the summary is uploaded. Due to this differing flow some drivers, like odsp, create files with a .tmp extension appended to the file name, this is meant to signify that that file could be incomplete. For example, the summary could fail to upload after blobs have been uploaded, and this will not be a valid fluid file. it is expected that the application will rename the file after attachment completes if the .tmp extension is not desired. If an application does not expect the .tmp extension this can create issues, so for now, we will put this support under a flag, that must be explicitly enabled "Fluid.Container.MemoryBlobStorageEnabled" = true so that apps must opt into this behavior.

related to #21144

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +501 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	451.96 KB	451.96 KB	■ No change
azureClient.js	550.38 KB	550.55 KB	⯅ +167 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	255.82 KB	255.82 KB	■ No change
fluidFramework.js	374.96 KB	374.96 KB	■ No change
loader.js	133.27 KB	133.43 KB	⯅ +167 Bytes
map.js	41.12 KB	41.12 KB	■ No change
matrix.js	143.41 KB	143.41 KB	■ No change
odspClient.js	518.46 KB	518.62 KB	⯅ +167 Bytes
odspDriver.js	97.26 KB	97.26 KB	■ No change
odspPrefetchSnapshot.js	42.24 KB	42.24 KB	■ No change
sharedString.js	159.92 KB	159.92 KB	■ No change
sharedTree.js	374.95 KB	374.95 KB	■ No change
Total Size	3.22 MB	3.22 MB	⯅ +501 Bytes

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Baseline commit: 786b7d0

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