Harden storage filter column handling

[Rello]

Motivation

• Prevent misuse of filter keys in storage queries by allowlisting allowed columns and avoid injecting arbitrary identifiers into SQL.
• Improve observability by logging blocked unsupported filter columns to detect suspicious inputs.

Description

• Add FILTERABLE_COLUMNS allowlist constant with dimension1, dimension2, timestamp, and value.
• Add getAllowedFilterColumn() helper that checks the allowlist and logs blocked columns via logger.
• Validate filter keys in read() and sqlWhere() by replacing direct usage of the filter key with the allowed column and skipping unsupported ones, and update SQL expressions to use the validated column.
• Update CHANGELOG.md to document the hardening.

Testing

• No automated tests were run.

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