Update OperationRateLimiting docs for partition key normalization

[maliming]

Document the normalization behavior for PartitionByEmail and PartitionByPhoneNumber, and add a warning for PartitionByParameter about manual normalization of user-supplied values.

[Copilot]

Pull request overview

Updates the Operation Rate Limiting documentation to clarify how partition keys are normalized (or not) across built-in partitioning helpers, helping developers avoid unintentionally splitting counters due to inconsistent user input formatting/casing.

Changes:

• Added an explicit warning that PartitionByParameter uses the raw parameter value without normalization.
• Documented that PartitionByEmail normalizes to uppercase using ToUpperInvariant().
• Documented that PartitionByPhoneNumber normalizes by stripping common formatting characters while preserving + and digits.