Meta: Refactor pipeline aggregations

[wchaparro]

There are a number of issues related to pipeline/bucket aggregations. We've been tracking these and believe that there is value in a refactor to reduce the issues, as well as ensure that future changes won't break things. This meta issue is for tracking these related issues.

• [x] https://github.com/elastic/elasticsearch/issues/76320
• [ ] https://github.com/elastic/elasticsearch/issues/62731
• [x] https://github.com/elastic/elasticsearch/issues/72983
• [ ] https://github.com/elastic/elasticsearch/issues/23874
• [x] https://github.com/elastic/elasticsearch/issues/14600
• [ ] https://github.com/elastic/elasticsearch/issues/60021
• [ ] https://github.com/elastic/elasticsearch/issues/36487
• [ ] Make bucketsPath syntax for lower and upper standard deviation bounds in the extended_stats aggregation more obvious
• [ ] https://github.com/elastic/elasticsearch/issues/32692
• [ ] https://github.com/elastic/elasticsearch/issues/66677
• [ ] https://github.com/elastic/elasticsearch/issues/63083
• [x] https://github.com/elastic/elasticsearch/issues/73429
• [ ] https://github.com/elastic/elasticsearch/issues/52522
• [ ] https://github.com/elastic/elasticsearch/issues/52491
• [ ] https://github.com/elastic/elasticsearch/issues/52449

[elasticmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[ajosh0504]

I just created this issue which might be relevant to add to the above list as well? : https://github.com/elastic/elasticsearch/issues/83474

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)