Member enrichment upsert by existing platform instead of GitHub

[epipav]

• Enrichment service was trying to upsert the member with GitHub platform always - This was causing a problem when the member was enriched by e-mail and didn't have any GitHub identities before. We were trying to upsert the member using the GitHub platform, and memberExists function was failing to return the existing member.
  Now we try to upsert the existing member with the first identity of the member instead of GitHub.

Changes proposed ✍️

What

🤖 Generated by Copilot at cfd812e

Improved the member service to handle different platforms and avoid errors. Refactored the memberService.upsert method and added a check for response.profile in memberEnrichmentService.ts.
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🤖 Generated by Copilot at cfd812e

We are the members of the service
We rise from different platforms
We don't need no profile data
We upsert with our usernames

Why

How

🤖 Generated by Copilot at cfd812e

• Enable upserting members from different platforms (link)
• Fix possible error when accessing profile data (link)

Checklist ✅

• Label appropriately with Feature, Improvement, or Bug.
• Add screehshots to the PR description for relevant FE changes
• New backend functionality has been unit-tested.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.