feat: CE-1045 Add getLeadsByActionTaken query

[mikevespi]

Description

In order for users to be able to filter complaints by action taken in NATCom, a function to return the list of lead_identifiers that belong to case_files that have had that action taken on them was needed. Current implementation aims to avoid raw querying the database via TypeORM, but the result is 3 separate calls. Refactoring to a single query handled with joins may be a good idea, however the impact of raw queries can cause problem with some ORMs. Worth looking into, for now this follows existing pattern in the code base.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested manually, and in e2e tests found in NATCom PR bcgov/nr-compliance-enforcement#707

Checklist

• I have read the CONTRIBUTING doc
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have already been accepted and merged

Further comments

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