Implement quote_keys flag for std functions manifestYamlDoc/manifestY…

[jnyi]

…amlStream to match official jsonnet doc

Purpose

This PR creates a flag documented in jsonnet official site std library: https://jsonnet.org/ref/stdlib.html for function manifestYamlDoc and manifestYamlStream, it will allow us to generate yaml without quoting the keys.

Test

• Tested via unit tests.
• compile sjsonnet using ./mill -i show "sjsonnet[2.13.4]".jvm.assembly and run again a locally created test.jsonnet to output YAML via flag --yaml-out

[lihaoyi-databricks]

Passing the review to @szeiger