Change the log level of adding credits from Info to Debug

[liukun-msft]

Description

Stress tests found that there were too many add credit logs.

• Eventhubs processor can create ~500MB of logs per day logs , most of which are:

• Servicebus processor can create ~200MB of logs per day, most of which are:

It is also mentioned in the log tuning issue: #20836 (comment)

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.

[azure-sdk]

API change check

API changes are not detected in this pull request.