feat: cache hits in expr context docs

[SkArchon]

Description

This PR adds docs for the new attributes in the expr context for cache hit statuses. Depends on wundergraph/cosmo#2643

Summary by CodeRabbit

• Documentation
  • Added five new cache hit indicator fields to Operation object in template expressions: normalizationCacheHit, variablesNormalizationCacheHit, variablesRemappingCacheHit, persistedOperationCacheHit, and planCacheHit.
  • Updated examples demonstrating cache hit field usage.

Checklist

• I have validated my changes locally using mintlify dev
• I have validated my changes are working as expected by looking at the preview deployment
• All links in my documentation work correctly
• All images render properly
• Code examples are tested and formatted correctly
• If I added new pages, they are included in the navigation (docs.json)

[coderabbitai]

Walkthrough

Documentation update adding five new boolean cache-related fields to the Operation object in template expressions: normalizationCacheHit, variablesNormalizationCacheHit, variablesRemappingCacheHit, persistedOperationCacheHit, and planCacheHit. Example expressions updated to demonstrate planCacheHit usage.

Changes

Cohort / File(s)	Summary
Documentation Updates docs/router/configuration/template-expressions.mdx	Adds five new boolean fields (normalizationCacheHit, variablesNormalizationCacheHit, variablesRemappingCacheHit, persistedOperationCacheHit, planCacheHit) to Operation object reference documentation and updates example expressions to demonstrate planCacheHit usage.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding documentation for cache hit fields in the expression context for the router configuration.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

📝 Coding Plan

• Generate coding plan for human review comments

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