Enable destination_project_quota for logs exporter

[damemi]

Fixes #558

Adding this was pretty simple, the current logic builds a single LogEntry list and then batches those entries as needed to keep each batch request under the GCP size limit. We can do this without caring about the project for each entry because, while batch LogEntry requests do have a field for project, the request will honor individual project IDs set on each entry in the batch. (Traces and Metrics don't have that)

However, adding destination project quota brings us back to caring about the project at the request/batch level. That's easy to do using a map[string]LogEntry, which is similar to how traces and metrics batch.

But, it would be optimal to revert to the efficient, possibly mixed-project batching when destination_project_quota is disabled. The best I could think of to do this is to drop everything in a single key in the map, and reuse the rest of the logic. I'm not very satisfied with that, because I don't like using a magic key and it couples the destination_project_quota config option to multiple places in the code. So this might be more refactorable, but for unblocking the feature this will do fine imo, but I'm open to ideas

edit: to get CI to pass I had to add the service usage consumer role to our GCP service account in the second project

[damemi]

note that this fixture differs from logs_multi_project_expected.json here, with 2 lists of entries

[codecov]

Codecov Report

Merging #579 (0c934b2) into main (e169468) will decrease coverage by 0.17%.
The diff coverage is 6.97%.

❗ Current head 0c934b2 differs from pull request most recent head 46a5f41. Consider uploading reports for the commit 46a5f41 to get more accurate results

@@            Coverage Diff             @@
##             main     #579      +/-   ##
==========================================
- Coverage   64.12%   63.95%   -0.17%     
==========================================
  Files          38       38              
  Lines        4318     4334      +16     
==========================================
+ Hits         2769     2772       +3     
- Misses       1432     1445      +13     
  Partials      117      117              

Impacted Files	Coverage Δ
exporter/collector/logs.go	39.07% <0.00%> (-1.63%)	⬇️
...lector/integrationtest/testcases/testcases_logs.go	100.00% <100.00%> (ø)

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[dashpole]

looks great.

[damemi]

I think the test-coverage failure is https://community.codecov.com/t/upload-issues-unable-to-locate-build-via-github-actions-api/3954/10. Regardless, that's non blocking