Add new alteration counts endpoint

[onursumer]

Related to #9305

• Add an endpoint to fetch alteration counts by gene
• Request parameters are entrez gene ids, molecular profile case identifiers, and an alteration filter.
• Fetching by study or cohort is not supported yet.

[onursumer]

Looks like changes introduced by https://github.com/cBioPortal/cbioportal/commit/ad8f6f5ae59afd4ffe35b781236c447af7498a76 causing discrepancy between the frontend and the backend when calculating the number of profiled cases for multiple studies.

We can solve the issue by reverting it back and use casesWithoutPanelData, but we probably should do it when the method is called only for this endpoint.

[sonarqubecloud[bot]]

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