Cleanup and improvements for simple version of patterned_text

[parkertimmins]

• Update arguments encoding to separate doc value for faster merge - Encode args in a schema doc value rather than using placeholders #132782
• Add patterned_text to data generation tests. Since patterned_text can only have one value per document, this will require some changes to testing framework.
• Benchmark query performance. elastic/logs does query all default fields, but some patterned_text specific queries would be ideal.
• Benchmark a large number of templates. wikipedia rally tracks may be suitable for this.
• Add documentation

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)