Update document for firewall lifetime connection limit

[TD2106]

Add new screenshot and description for firewall config

[prmerger-automator]

@TD2106 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change. @biqian

[learn-build-service-prod]

Learn Build status updates of commit a974f6f:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/azure-signalr/media/signalr-howto-config-application-firewall/signalr-add-application-firewall-rule.png	✅Succeeded
articles/azure-signalr/signalr-howto-configure-application-firewall.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.
Image File	This PR added or updated an image file(s).

[ShannonLeavitt]

@bjqian

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[learn-build-service-prod]

Learn Build status updates of commit dd4ad74:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/azure-signalr/media/signalr-howto-config-application-firewall/signalr-add-application-firewall-rule.png	✅Succeeded
articles/azure-signalr/signalr-howto-configure-application-firewall.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.
Image File	This PR added or updated an image file(s).

[v-dirichards]

@bjqian I'll merge this PR based on your approval. If this article requires further changes, please open a separate pull request.