feat(openapi): Implement getIndexSizes function from rest.li in openapi

[iprentic]

• Move this function over here as we want to use openapi moving forward
• It can be used in a health check (though it has authentication)

Url: http://localhost:9002/openapi/operations/elasticSearch/getIndexSizes
Output:

"sizes":[{"aspectName":"datahubingestionrunsummary","entityName":"datajob","indexName":"datajob_datahubingestionrunsummaryaspect_v1","sizeMb":0.208},{"aspectName":"dashboardusagestatistics","entityName":"dashboard","indexName":"dashboard_dashboardusagestatisticsaspect_v1","sizeMb":0.208},{"aspectName":"datasetprofile","entityName":"dataset","indexName":"dataset_datasetprofileaspect_v1","sizeMb":0.208},{"aspectName":"chartusagestatistics","entityName":"chart","indexName":"chart_chartusagestatisticsaspect_v1","sizeMb":0.208},{"aspectName":"datahubingestioncheckpoint","entityName":"datajob","indexName":"datajob_datahubingestioncheckpointaspect_v1","sizeMb":0.208},{"aspectName":"assertionrunevent","entityName":"assertion","indexName":"assertion_assertionruneventaspect_v1","sizeMb":0.208},{"aspectName":"dataprocessinstancerunevent","entityName":"dataprocessinstance","indexName":"dataprocessinstance_dataprocessinstanceruneventaspect_v1","sizeMb":0.208},{"aspectName":"operation","entityName":"dataset","indexName":"dataset_operationaspect_v1","sizeMb":0.208},{"aspectName":"datasetusagestatistics","entityName":"dataset","indexName":"dataset_datasetusagestatisticsaspect_v1","sizeMb":0.208}]}

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub