Add missing metric documentions

[sgiehl]

Description:

This PR significantly improves metric documentation by adding many missing entries and enhancing existing ones. Additionally, it introduces a major overhaul in how the metric glossary is generated.

Key Changes

1. Improved Metric Documentation

   • Added missing metric descriptions.
   • Enhanced clarity and accuracy of existing documentation.

2. Revamped Metric Glossary Generation

   • The previous approach iterated over all available reports, adding/updating metrics as they appeared. This meant the last processed report effectively determined the name and documentation of a metric, which led to inconsistencies.
   • The new approach first collects all globally defined metrics and their documentation. It then iterates over reports to capture any additional metrics while preserving report-specific documentation.
   • If a metric lacks a global default description, the system checks report-specific descriptions. If more than 50% of reports use the same definition, that becomes the default.
   • Metrics without a sufficiently consistent definition are removed from the glossary to avoid ambiguity.

Impact

These changes ensure that the glossary provides accurate and reliable metric definitions, reducing inconsistencies caused by report-specific variations.

Note

The changes are causing some test failures in submodule, which we need to resolve after review, but before merging.

fixes #17230

Review

• Functional review done
• Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• Documentation added if needed
• Existing documentation updated if needed