Remove unnecessary warnings in administration client

[conniey]

Description

• Removes extraneous log messages when creating subscription or topics. Since support of default rule in subscriptions, it is possible to not see a RuleAction or RuleFilter in the XML. This should not return a WARN.
• For missing entities, the service can return an entry with no content.

Fixes #32325

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
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Testing Guidelines

• Pull request includes test coverage for the included changes.

[anuchandy]

thanks lgtm!

[azure-sdk]

API change check

API changes are not detected in this pull request.