[port 2.3]: 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	460.88 KB	460.92 KB	⯅ +35 Bytes
azureClient.js	559.03 KB	559.08 KB	⯅ +49 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	261.68 KB	261.69 KB	⯅ +14 Bytes
fluidFramework.js	401.54 KB	401.56 KB	⯅ +14 Bytes
loader.js	134.17 KB	134.19 KB	⯅ +14 Bytes
map.js	42.43 KB	42.44 KB	⯅ +7 Bytes
matrix.js	146.59 KB	146.6 KB	⯅ +7 Bytes
odspClient.js	526.18 KB	526.23 KB	⯅ +49 Bytes
odspDriver.js	97.8 KB	97.82 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.76 KB	42.78 KB	⯅ +14 Bytes
sharedString.js	163.27 KB	163.28 KB	⯅ +7 Bytes
sharedTree.js	392.01 KB	392.02 KB	⯅ +7 Bytes
Total Size	3.3 MB	3.3 MB	⯅ +245 Bytes

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Baseline commit: e8b5a74

Generated by 🚫 dangerJS against d4dbd31

[frankmueller-msft]

Approved