Add index to foreign key (parent_id) column for optimized record retrieval & deletion

[akhil018]

The problem was identified in the foreign key(parent_id) column, where retrieval and deletion of records took an unexpectedly long time. To optimize the retrieval and deletion process, this fix introduces a new index on the relevant foreign key (parent_id) column.

This commit addresses performance issues related to both record deletion and retrieval in the sqlalchemy_mptt library. Adding an index to the foreign key(parent_id) column improves the efficiency of both operations, significantly reducing the time taken for deletion and retrieval.