[#6643] WithManagedIdentity is experimental and not exist in Microsoft.Identity.Client 4.51.0

[sw-joelmut]

Fixes #6643

Description

This PR updates the Microsoft.Identity.Client package from 4.50 to 4.55 to implement the official MSI functionality.

Specific Changes

• Replaced IConfidentialClientApplication with IManagedIdentityApplication.
• Replaced AcquireTokenForClient with AcquireTokenForManagedIdentity due to the new application type.
• Removed unused _appId property.
• Removed experimental flag.
• Removed scopes, only the resource is required.

Testing

The following image shows the bot working with the new implementation.

[sw-joelmut]

Hi @tracyboehrer, there's a problem with the CI pipeline in this PR. We think it is related to the new version of Microsoft.Identity.Client not being available in the custom NuGet feed.
Thanks.

[tracyboehrer]

@sw-joelmut This PR is failing due to what @Danieladu is working on in #6687. Though that PR isn't currently building. Perhaps some coordination is in order.

[tracyboehrer]

@sw-joelmut This is failing due to some Microsoft.Bot.Connector.Tests failures.

[coveralls]

Pull Request Test Coverage Report for Build 369407

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.006%) to 73.448%

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Files with Coverage Reduction	New Missed Lines	%
/libraries/integration/Microsoft.Bot.Builder.Integration.AspNet.Core/ServiceCollectionExtensions.cs	1	93.55%
/libraries/Microsoft.Bot.Connector.Streaming/Application/TimerAwaitable.cs	1	68.25%
/libraries/Microsoft.Bot.Connector/Authentication/ManagedIdentityAuthenticator.cs	3	86.11%

Totals
Change from base Build 369254:	-0.006%
Covered Lines:	24140
Relevant Lines:	32867

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💛 - Coveralls

[BruceHaley]

✔️ No Binary Compatibility issues for Microsoft.Bot.Connector.dll