Add documentation on testing BigQuery from ingestion-beam

[acmiyaguchi]

This adds some documentation on a workflow for testing against data in PubSub from the various sinks in ingestion-beam.

[jklukas]

Very nice. Thanks for adding this!

[jklukas]

Is it possible to decrease the font sizes? This is rendering strangely for me where most of the text looks clipped inside the boxes:

[acmiyaguchi]

It looks like this will fix it -- mermaid-js/mermaid#790 (comment)

The online editor does the right thing. I think the mermaid cli tool and the online tool are out of sync.

[jklukas]

It looks better for me now too.

[codecov-io]

Codecov Report

Merging #543 into master will decrease coverage by 6.23%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #543      +/-   ##
============================================
- Coverage     89.28%   83.05%   -6.24%     
+ Complexity      338      325      -13     
============================================
  Files            56       56              
  Lines          1894     1894              
  Branches        177      177              
============================================
- Hits           1691     1573     -118     
- Misses          139      265     +126     
+ Partials         64       56       -8

Flag	Coverage Δ	Complexity Δ
#ingestion_beam	80.36% <ø> (-7.22%)	325 <ø> (-13)
#ingestion_edge	100% <ø> (ø)	0 <ø> (ø)	⬇️

Impacted Files	Coverage Δ	Complexity Δ
...m/src/main/java/com/mozilla/telemetry/io/Read.java	50% <0%> (-50%)	1% <0%> (ø)
.../telemetry/transforms/PubsubMessageToTableRow.java	38.23% <0%> (-33.83%)	23% <0%> (-10%)
.../src/main/java/com/mozilla/telemetry/io/Write.java	66.02% <0%> (-28.21%)	1% <0%> (ø)
...ozilla/telemetry/transforms/PubsubConstraints.java	53.65% <0%> (-26.83%)	7% <0%> (ø)
...java/com/mozilla/telemetry/options/OutputType.java	78.94% <0%> (-21.06%)	1% <0%> (ø)
.../java/com/mozilla/telemetry/options/InputType.java	80% <0%> (-20%)	1% <0%> (ø)
...la/telemetry/transforms/MapElementsWithErrors.java	85.71% <0%> (-10.72%)	4% <0%> (ø)
...ava/com/mozilla/telemetry/options/SinkOptions.java	72% <0%> (-8%)	5% <0%> (-2%)
...mozilla/telemetry/transforms/LimitPayloadSize.java	92.85% <0%> (-7.15%)	4% <0%> (-1%)

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