Added various metrics to SearchContext.

[rwiker]

Issue

N/A

Short description

Adds various metrics aggregation to search contexts, specifically, "min", "max", "avg", "sum", "stats", "extended_stats",
"percentiles", "value_count" and "cardinality". These are accessed through the metrics member on class SearchContext. See examples in examples/metrics.ipynb.

Pre-review checklist

• Read through all changes. No redundant print() statements, commented-out code, or other remnants from the development. 👀
• Make sure tests pass after every commit. ✅
• New/refactored code is following same conventions as the rest of the code base. 🧬
• New/refactored code is tested. ⚙
• Documentation has been updated 🧾

Pre-merge checklist

• Commit history is consistent and clean. 👌

[equinor-ruaj]

👍

[equinor-ruaj]

lgtm