CRINGE-8: update eliot architecture diagram

[biancadanforth]

Because:

• Eliot's architecture diagram hasn't been updated since it was migrated from AWS to GCP in 2023.
• We need an updated architecture diagram for Eliot's Service Overview document.

This PR:

• Updates Eliot's architecture diagram in the docs.

PR notes:

• I used drawio which is the tool we've used for architecture diagrams in the past in Crash Ingestion.
• I didn't change much from the old diagram:
  • Replaced AWS ELB with GCLB (@smarnach : did I get the name of the GCLB right?).
  • Removed "browser" from the example clients and added "profiler".
  • Fixed some style issues -- mostly made the background white, so the diagram is visible on any background.

Once this PR is approved and merged:

• Update the architecture diagram in Eliot's infra / admin guide
• Update the architecture diagram in Eliot's Service Overview document