CI Step output file should accept a series of JSON lines

Problem

The CI Step ${{output_file}} is structured using the following format:

[key]=[JSON value]\n
[key]=[JSON value]\n
...

For example:

dir="/path/to/dir"\n
messages=[{"name":"fred","message":"Hello"}]\n

This format is not extensible, so additional metadata cannot be supplied when writing the value. Example metadata may include whether the value has changed, the time the value was written, if the value is sensitive, etc.

Proposal

Change the format of the output file to be entirely JSON:

[JSON object]\n
[JSON object]\n
...

For example:

{"name":"dir","value":"/path/to/dir"}\n
{"name":"messages","value":[{"name":"fred","message":"Hello"}]}\n

Step authors can use the above format to add additional metadata, for example:

{"name":"dir","value":"/path/to/dir","sensitive":false}\n