Add comprehensive aggregation support

[sdqri]

Summary

• Add broad aggregation coverage across metrics, bucket, and pipeline aggregations
• Expand aggregation test coverage with doc-style option cases
• Reorganize aggregation docs navigation and publish updated docs output

Testing

• go test ./...

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 33.69376% with 1901 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
aggregations/aggregation.go	0.00%	106 Missing ⚠️
...tions/bucket/significantterms/significant_terms.go	15.58%	55 Missing and 10 partials ⚠️
...ggregations/bucket/datehistogram/date_histogram.go	18.84%	54 Missing and 2 partials ⚠️
aggregations/bucket/histogram/histogram.go	18.51%	42 Missing and 2 partials ⚠️
aggregations/bucket/multiterms/multi_terms.go	16.98%	42 Missing and 2 partials ⚠️
...gations/bucket/significanttext/significant_text.go	16.98%	42 Missing and 2 partials ⚠️
aggregations/metrics/weightedavg/weighted_avg.go	37.93%	32 Missing and 4 partials ⚠️
...ns/bucket/autodatehistogram/auto_date_histogram.go	23.80%	30 Missing and 2 partials ⚠️
aggregations/bucket/geodistance/geo_distance.go	25.58%	30 Missing and 2 partials ⚠️
aggregations/bucket/rareterms/rare_terms.go	21.95%	30 Missing and 2 partials ⚠️
... and 65 more
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Files with missing lines	Coverage Δ
aggregations/bucket/children/children.go	30.43% <30.43%> (ø)
aggregations/bucket/filter/filter.go	36.00% <36.00%> (ø)
aggregations/bucket/global/global.go	23.80% <23.80%> (ø)
aggregations/bucket/missing/missing.go	36.00% <36.00%> (ø)
aggregations/bucket/nested/nested.go	30.43% <30.43%> (ø)
aggregations/bucket/parent/parent.go	30.43% <30.43%> (ø)
aggregations/bucket/sampler/sampler.go	36.00% <36.00%> (ø)
aggregations/bucket/terms/terms.go	79.22% <79.22%> (ø)
aggregations/metrics/boxplot/boxplot.go	56.75% <56.75%> (ø)
...ations/metrics/cartesianbounds/cartesian_bounds.go	36.00% <36.00%> (ø)
... and 65 more

... and 35 files with indirect coverage changes

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