[BUG] Make AsyncUploadMockFsRepo work with RemoteCloneIndexIT and RemoteSplitIndexIT

[gbbafna]

Describe the bug

Coming from #15037

If we use asyncUploadMockFsRepo=true , we get transient translog upload failures due to checksum coming null. We need to fix this inorder to enable testCreateCloneIndexLowPriorityRateLimit which only works with AsyncMultiStreamBlobContainer

See #15107 as well

Related component

Storage:Durability

To Reproduce

see the failing builds in #14292

Expected behavior

Tests should pass with asyncUploadMockFsRepo=true

Additional Details

NA