build: use synth templates and kokoro config

[JustinBeckwith]

This brings in the kokoro configuration we're using for all of our other libraries, along with other common templated files.

• blocked on getting the kokoro backend configured
• Submit PR to land just the formatting changes
• Submit PR to land just the formatting changes
• Get the unit tests all passing in kokoro
• Migrate remaining customized tests over to kokoro
• Delete circleCI config

[codecov]

Codecov Report

Merging #1049 into master will decrease coverage by 2.99%.
The diff coverage is 98.07%.

@@           Coverage Diff            @@
##           master    #1049    +/-   ##
========================================
- Coverage   94.85%   91.85%    -3%     
========================================
  Files          96      110    +14     
  Lines        6311     6517   +206     
  Branches      496      496            
========================================
  Hits         5986     5986            
- Misses        166      372   +206     
  Partials      159      159

Impacted Files	Coverage Δ
test/web-frameworks/restify.ts	88.23% <ø> (ø)	⬆️
src/plugins/plugin-bluebird.ts	100% <ø> (ø)	⬆️
src/config.ts	100% <ø> (ø)	⬆️
src/plugins/plugin-restify.ts	97.14% <ø> (ø)	⬆️
test/web-frameworks/connect.ts	76.92% <ø> (ø)	⬆️
test/web-frameworks/koa2.ts	76.92% <ø> (ø)	⬆️
src/cls/async-listener.ts	100% <ø> (ø)	⬆️
src/trace.ts	100% <ø> (ø)	⬆️
test/web-frameworks/express.ts	75.86% <ø> (ø)	⬆️
src/cls/null.ts	88.88% <ø> (ø)	⬆️
... and 67 more

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