DENG-9533 - Support ingesting Glean server pings submitted directly to Pub/Sub

[akkomar]

Description

Adds a third ingestion path to the Decoder job: messages published directly to Pub/Sub by server-side telemetry clients, bypassing Cloud Logging / fluentbit. Enabled at deploy time via a new --directPubsubEnabled=true flag (parallel to --logIngestionEnabled).

I intend to land this first, then prepare IAC config, land mozilla/glean_parser#821, and then test this in stage with MARS.

I have tested this end to end using template generated from mozilla/glean_parser#821 in a sandbox project: https://github.com/akkomar/glean-server-examples/tree/pubsub/test-go-publisher.

Related Tickets & Documents

• DENG-9533

Merging Guidelines

Changes affecting ingestion-edge

Code updates are always safe to merge since production code updates are always
deployed manually.

Changes affecting ingestion-sink

Code updates are always safe to merge since production code updates are always
deployed manually. See these instructions
for updating the code version.

Changes affecting ingestion-beam (including ingestion-core)

• Only merge changes to main that you want to propagate to production automatically
• Check pipeline latency before merging, particularly if:
  • The merge will occur within 2 hours of the UTC date change, or
  • You are merging multiple PRs in quick suggestion

See the full code deployment policy
for details.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.26%. Comparing base (5cd46c5) to head (55571f6).

Files with missing lines	Patch %	Lines
.../com/mozilla/telemetry/decoder/DecoderOptions.java	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2857      +/-   ##
============================================
+ Coverage     86.24%   86.26%   +0.02%     
- Complexity      885      891       +6     
============================================
  Files           118      119       +1     
  Lines          5075     5090      +15     
  Branches        518      520       +2     
============================================
+ Hits           4377     4391      +14     
- Misses          531      532       +1     
  Partials        167      167              

Flag	Coverage Δ
ingestion_beam	83.90% <86.66%> (+0.03%)	⬆️

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didn't mean to approve, just commenting