[v2] make job descriptor JSON5 compatible

[mimir-d]

Current state: the serialization/deserialization of JSON is done with the golang "encoding/json" package which only understands the standard ECMA flavor.
It has proven useful to have comments in the input descriptors, so we should use a format that supports that.

[xaionaro]

Current state: the serialization/deserialization of JSON is done with the golang "encoding/json" package which only understands the standard ECMA flavor.

IIRC, we had a consensus (in old discussions with @insomniacslk) to use YAML. It is human-readable, supports comments and is a superset for JSON.

[mimir-d]

well, we have both. And we can't just remove support for json now. This would at least get some parity.

[xaionaro]

We do not need the support of JSON, since it is a subset of YAML.