Allow KQL comments and let statements (#2385)

[xiangyan99]

• Allow KQL comments and let statements

• updates

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Pre-merge Checklist

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[Copilot]

Pull request overview

This PR updates the Kusto tool’s KQL query validation to support more idiomatic KQL authoring by allowing // comments and semicolon-separated let statements, while still blocking known-dangerous management commands and tautology-based injections.

Changes:

• Allow // comments in KQL inputs (previously rejected).
• Allow semicolons/let statements by removing the “multiple statements” rejection.
• Replace management-command detection with a whitespace-tolerant regex check (including tabs/newlines).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tools/Azure.Mcp.Tools.Kusto/src/Validation/KqlQueryValidator.cs	Removes comment/semicolon blocking and switches management-command detection to a regex-based approach.
tools/Azure.Mcp.Tools.Kusto/tests/Azure.Mcp.Tools.Kusto.UnitTests/KqlQueryValidatorTests.cs	Updates/extends unit tests to reflect newly-allowed comments and semicolons and adds whitespace variants for management-command detection.
servers/Azure.Mcp.Server/changelog-entries/1775838003897.yaml	Adds a changelog entry describing the KQL validator behavior changes.