Allow an additional retry for IMDS managed identity requests

[chlowell]

Closes #24842 with a small tweak to IMDS retry configuration. Our retry policy doesn't allow setting retry options based on a response, so this PR allows another retry in any case and shortens the MaxRetryDelay so the total retry period is about 70 seconds.

Here's a sample of the change's effect. Delays for retries 1-3 are unchanged (jitter causes the variation) but now there's a 5th retry, which like the 4th is limited to 25s.

Retry	Delay before	Delay after
1	2.11s	1.71s
2	5.69s	7.46s
3	12.37s	13.38s
4	31.80s	25.00s
5	—	25.00s
Total	51.97s	72.55s

[Copilot]

Pull Request Overview

This PR adjusts the IMDS retry behavior for ManagedIdentityCredential by extending the retry count, reducing the maximum backoff delay, and updating the changelog to reflect the new ~70-second retry window.

• Increased the default MaxRetries from 5 to 6
• Reduced the default MaxRetryDelay from 1 minute to 25 seconds
• Removed the default TryTimeout setting and documented the ~70s retry period in CHANGELOG

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
sdk/azidentity/managed_identity_client.go	Bumped default retries, shrank max delay, removed TryTimeout default
sdk/azidentity/CHANGELOG.md	Added entry noting ~70s total IMDS retry duration

Comments suppressed due to low confidence (2)

sdk/azidentity/managed_identity_client.go:84

• By removing the default TryTimeout, requests may no longer time out as intended and could hang indefinitely. Consider reinstating or documenting this default timeout behavior.

	}

sdk/azidentity/CHANGELOG.md:16

• The markdown bullet has an extra - after the diff marker (+-). Please correct it to a single - and ensure consistent indentation for the wrapped line.

- By default, `ManagedIdentityCredential` retries IMDS requests for a maximum of ~70 seconds as recommended