Support 'aggs' (aggregations) within bucket aggregations (#818)

* fix AggregationContainer bug?

There was a bug when running a test on bucket aggregation `term filter` followed by another aggregation where it was throwing a validation error ‘must not have more than 1 property` which was due to the merging of the `allOf` rule with `maxProperties: 1`

Tweaked the schema a little so we separate them where the aggregation can only be one type followed by `aggregates` or `aggs` combination as per what it was before

Signed-off-by: Xavian Ang <[email protected]>

* add support for 2nd aggregation in bucket aggs

This was also throwing validation error when doing a second aggregation within a bucket aggregation so just adding a `additionalProperties` in `SingleBucketAggregateBase`

Signed-off-by: Xavian Ang <[email protected]>

* added test case for aggs within bucket aggs

Signed-off-by: Xavian Ang <[email protected]>

* fix up formatting + update refs to movies

Signed-off-by: Xavian Ang <[email protected]>

* fix up delete path

Signed-off-by: Xavian Ang <[email protected]>

* tweak tests letter case to match elsewhere

Signed-off-by: Xavian Ang <[email protected]>

* add punctuation to fix CI

Signed-off-by: Xavian Ang <[email protected]>

* add line to changelog

Signed-off-by: Xavian Ang <[email protected]>

---------

Signed-off-by: Xavian Ang <[email protected]>

Author: xavianaxw

CHANGELOG.md

@@ -5,6 +5,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ## [Unreleased]
 
 ### Added
+- Added `aggs` alias for nested aggregations ([#818](https://github.com/opensearch-project/opensearch-api-specification/pull/818))
 - Added API specs for query groups lifecycle APIs ([#649](https://github.com/opensearch-project/opensearch-api-specification/pull/649))
 - Added Python and Ruby spec validators ([#646](https://github.com/opensearch-project/opensearch-api-specification/pull/646))
 - Added verbose output of the story being evaluated ([#646](https://github.com/opensearch-project/opensearch-api-specification/pull/646))