Epics not updated in the index when labels are deleted
What does this MR do and why?
When the Label gets deleted, we should remove this label_id from the label_ids field in the epics index.
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How to set up and validate locally
Make sure Elasticsearch is enabled.
- Pick any epic on the gdk. Attach any label to it.
- Check on the elastic search that the label_idsin theepicsindex has an array of all the labels attached to this epic.
- Now delete any label that is attached to this epic from the Manage>Labelssection.
- Now verify on Elasticsearch that the deleted label is not in the array of label_ids. It might take a few extra seconds to reflect the changes in the elasticsearch.
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
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I have evaluated the MR acceptance checklist for this MR. 
Related to #424198 (closed)
Edited  by Ravi Kumar