docs: add metric engine sparse primary key encoding configuration

[Copilot]

What's Changed in this PR

Documents the metric engine's sparse primary key encoding feature enabled by default in GreptimeDB PR #7195.

Configuration Documentation (configuration.md)

• Updated region engine section to include metric engine alongside mito
• Added metric engine configuration section with sparse_primary_key_encoding option (default: true)
• Documented performance benefits: encodes only non-null primary key columns to reduce CPU overhead

Metric Engine Documentation (metric-engine.md)

• Updated operational capabilities to reflect DELETE support on logical tables
• Clarified physical tables remain read-only for safety

Applied to both nightly and v1.0 documentation versions in English and Chinese (中文).

Chinese Documentation (中文文档)

• Updated configuration documentation with metric engine section and sparse_primary_key_encoding option
• Updated metric engine documentation to reflect DELETE support on logical tables
• Applied to both current (nightly) and version-1.0

Checklist

• Please confirm that all corresponding versions of the documents have been revised.

• Please ensure that the content in sidebars.ts matches the current document structure when you changed the document structure.

• This change requires follow-up update in localized docs.

• Fixes Update docs for feat(metric)!: enable sparse primary key encoding by default #2200

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update docs for feat(metric)!: enable sparse primary key encoding by default</issue_title>
<issue_description>A document change request is generated from GreptimeTeam/greptimedb#7195</issue_description>

<agent_instructions>Update nightly and v1.0, following existing markdown write styling</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Update docs for feat(metric)!: enable sparse primary key encoding by default #2200

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View logs

[WenyXu]

@copilot update Chinese version

[Copilot]

@copilot update Chinese version

Updated Chinese documentation in commit 8bee8ca. Changes include:

• Configuration documentation with metric engine section and sparse_primary_key_encoding option
• Metric engine documentation reflecting DELETE support on logical tables
• Applied to both current (nightly) and version-1.0

[fengjiachun]

LGTM