This also seems to squash a stubborn space leak we see with
subscriptions (linking to canonical #3388 for reference).
This may also fix some of the "Unexpected exception" websockets
exceptions we are now surfacing (see e.g. #4344)
Also: dev.sh: fix hpc reporting
Initial work on this done by Vamshi.
* export metadata without nulls, empty arrays
* property tests for 'ReplaceMetadata' using QuickCheck
-> Derive Arbitrary class for 'ReplaceMetadata' dependant types
* reduce property test cases number to 30
QuickCheck generates the `ReplaceMetadata` value really large
for higher number test cases. Encoded JSON for such values is large and
consumes more memory. Thus, CI is giving up while running property
tests.
* circle-ci: Add property tests as saperate job
* add no command mode to tests
* add yaml.v2 to go mod
* remove indirect comment for yaml.v2 dependency
