[port 2.2]: Avoid two leading slashes in the request to create a new file (#22563)

[sonalideshpandemsft]

Cherry-pick: #22563

[github-actions]

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[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +245 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	457.92 KB	457.96 KB	⯅ +35 Bytes
azureClient.js	555.24 KB	555.29 KB	⯅ +49 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	258.73 KB	258.75 KB	⯅ +14 Bytes
fluidFramework.js	406.01 KB	406.02 KB	⯅ +14 Bytes
loader.js	134.2 KB	134.22 KB	⯅ +14 Bytes
map.js	42.25 KB	42.25 KB	⯅ +7 Bytes
matrix.js	146.42 KB	146.42 KB	⯅ +7 Bytes
odspClient.js	523.38 KB	523.43 KB	⯅ +49 Bytes
odspDriver.js	97.66 KB	97.68 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.72 KB	42.73 KB	⯅ +14 Bytes
sharedString.js	163.12 KB	163.13 KB	⯅ +7 Bytes
sharedTree.js	396.52 KB	396.53 KB	⯅ +7 Bytes
Total Size	3.3 MB	3.3 MB	⯅ +245 Bytes

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Baseline commit: 59cbe15

Generated by 🚫 dangerJS against 6d9ad73

[frankmueller-msft]

Approved