MQE: trim the label values condition for the labeled metrics query to enhance the readability.

[wankai123]

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Closes #.
• Update the CHANGES log.

[Copilot]

Pull request overview

This PR enhances the labeled metrics query functionality in MQE by replacing the basic split() method with Guava's Splitter API, which automatically trims whitespace and omits empty strings from the parsed label values. This improves query robustness and readability by handling label value inputs more gracefully.

Changes:

• Replaced String.split() with Splitter.on(separator).omitEmptyStrings().trimResults() in the buildLabelIndex method
• Added necessary Guava imports (Splitter and Iterables)
• Updated CHANGES.md to document the enhancement

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/query/IMetricsQueryDAO.java	Enhanced label value parsing to trim whitespace and filter empty strings using Guava Splitter
docs/en/changes/changes.md	Added changelog entry describing the enhancement

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