Add GHA coordinator for performance evaluation task scatter/gather

[cjonas9]

What

Creates a GHA coordinator that launches the tasks of the on-release performance evaluation suite and collects their results.

Adds baselines for the apply-load ingest load test (#741).

The architecture of the coordinator, as well as the changes made to the apply-load ingest load test (so that it would fit well with the coordinator), is as follows:

flowchart TB
  subgraph glue[".github/workflows/ — irreducible glue (YAML)"]
    coord["release-evaluation.yml<br/>build · areas · apply-load · report"]
    lt["load-test.yml<br/>dispatch EC2 · upload artifacts"]
  end

  subgraph pkg["cmd/stellar-rpc/internal/releaseeval/ — NEW: all logic + config"]
    eval["eval.go<br/>PerfReport schema · thresholds · compare"]
    rep["report.go<br/>render · aggregate · runGate"]
    thr["thresholds.json (//go:embed)"]
    gate["gate_test.go<br/>TestReleaseGate (env-gated entrypoint)"]
    unit["eval_test.go (unit tests)"]
  end

  subgraph it["cmd/stellar-rpc/internal/integrationtest/"]
    al["ingest_loadtest_test.go"]
  end

  ec2["EC2 box: run-load-test.sh<br/>runs apply-load test → bench-results.json"]

  coord -- "report job:<br/>go test -run TestReleaseGate" --> gate
  coord -- "apply-load job" --> lt --> ec2
  ec2 -- "bench-results.json + area-*/status.json<br/>(artifacts)" --> gate
  gate --> rep --> eval
  thr -. embedded .-> eval
  unit --> eval
  al == "imports PerfReport schema  ★ #741 edit" ==> eval
  ec2 -. "builds & runs" .-> al

  classDef edit741 fill:#ffe0e0,stroke:#cc0000,stroke-width:3px,color:#000;
  class al edit741;

Loading

Why

[TODO]

Known limitations

N/A. Remaining work for the epic this task is a part of mainly includes finishing off the other perf eval tasks (only the ingest load test is complete at this point).