docs: Add TQL value aliasing documentation for EVAL command

[Copilot]

This PR updates the TQL documentation to reflect the new value aliasing feature introduced in GreptimeTeam/greptimedb#7041.

Changes

Updated EVAL Syntax

The TQL EVAL command now supports an optional AS alias clause to provide meaningful names for query results:

TQL [EVAL | EVALUATE] (start, end, step) expr [AS alias]

Added Documentation and Examples

• Added explanation of the optional AS alias clause in the syntax section
• Included a practical example showing the feature in action:

  TQL eval (0, 10, '5s') {__name__="test"} AS test_series;

• Updated both English and Chinese documentation for consistency

Files Updated

• Current and v0.17 English documentation
• Current and v0.17 Chinese documentation

The documentation now accurately reflects this enhancement, allowing users to create more readable query results by providing custom column names instead of relying on default naming conventions.

Verification

• ✅ Documentation builds successfully
• ✅ Markdown formatting validated
• ✅ Multilingual consistency maintained

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update docs for feat: supports value aliasing in TQL</issue_title>
<issue_description>A document change request is generated from GreptimeTeam/greptimedb#7041</issue_description>

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

Fixes #2156

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[killme2008]

Looks good. It's a draft, i will update it after the PR are merged.