Release notes for 1.8.5, 1.8.6 and 1.8.7

[priyanshi-yb]

Describe the changes in this pull request

Added release notes in the RELEASE_NOTES.md

Describe if there are any user-facing changes

N/A

How was this pull request tested?

N/A

Does your PR have changes that can cause upgrade issues?

Component	Breaking changes?
MetaDB	No
Name registry json	No
Data File Descriptor Json	No
Export Snapshot Status Json	No
Import Data State	No
Export Status Json	No
Data .sql files of tables	No
Export and import data queue	No
Schema Dump	No
AssessmentDB	No
Sizing DB	No
Migration Assessment Report Json	No
Callhome Json	No
YugabyteD Tables	No
TargetDB Metadata Tables	No