[STRMCMP-610] Fix flink config rendering

[mwylde]

Flink's config format looks like YAML, but is not really YAML. The parser is extremely simple, and basically operates just by splitting each line on : and treating the first part as a key and the second as the value.

Currently we are using gopkg.in/yaml.v2 to render the config. However, this breaks in the case of long strings with spaces (like

-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=39000 -XX:+UseG1GC

). In that case, yaml.v2 will convert the space into a line break (go-yaml/yaml#166), producing output like

env.java.opts.jobmanager: -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=39000
  -XX:+UseG1GC

This is valid YAML, but cannot be handled by flink's simple parser.

This PR fixes the issue by doing the printing ourselves. As flink only supports simple key-value pairs in its config, this is pretty straightforward and more correct than using a real YAML library.

This is an incompatible change for apps that have a long, space-separated config