fix(resource-detector): map metadata server's instanceID to faas.id instead of faas.instance_id

[aabmass]

This matches the current Go/collector impl:

• faas.go in operations-go
• gcp.go in collector-contrib

This looks like a bug copied from the original Go impl https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/4e508ee3bbb979320283005464642e7d1afd0842/detectors/gcp/faas.go#L59-L62

[codecov]

Codecov Report

Merging #638 (a2e4e8d) into main (2e789b0) will not change coverage.
The diff coverage is 100.00%.

❗ Current head a2e4e8d differs from pull request most recent head 93f6316. Consider uploading reports for the commit 93f6316 to get more accurate results

@@           Coverage Diff           @@
##             main     #638   +/-   ##
=======================================
  Coverage   97.69%   97.69%           
=======================================
  Files          18       18           
  Lines         693      693           
  Branches      129      129           
=======================================
  Hits          677      677           
  Misses         16       16           

Files	Coverage Δ
...entelemetry-resource-util/src/detector/detector.ts	100.00% <100.00%> (ø)
...s/opentelemetry-resource-util/src/detector/faas.ts	96.15% <100.00%> (ø)

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[aabmass]

Ok now this causes tests to fail because the e2e test runner is expecting faas.instance after all: https://github.com/GoogleCloudPlatform/opentelemetry-operations-e2e-testing/blob/d72a3b50c2e9506009c89a831b435c795edcb9c8/trace_test.go#L258

And that is what we send in SDK detector: https://github.com/open-telemetry/opentelemetry-go-contrib/blob/8a2f8cfc4ac7dd7b9c1771cfbff2676f7777652e/detectors/gcp/detector.go#L63C25-L63C25

Will open a separate issue to discuss

[aabmass]

Oops I'm just confused GoogleCloudPlatform/opentelemetry-operations-go#679