OKR for GitLab: Add ability to filter project Work Items by type "Key Result"
Summary
The Project.workItems query allows fetching all Work Item objects present in a project, additionally, it supports type variable to provide list of IssueType values to filter the list with a specific Work Item type. Currently, the supported types are as follows;
INCIDENTISSUEOBJECTIVEREQUIREMENTTASKTEST_CASE
Proposal
We need to add support for KEY_RESULT enum for IssueType (potentially in app/graphql/types/issue_type_enum.rb) as that will allow Project.workItems query to filter the list with Key Result as criteria. We can refer to !103355 (merged) as a reference for implementing this enum since it added OBJECTIVE enum similarly.
This is necessary for Existing key result option to work in Work Items OKR Hierarchy Widget.
