JSON to ParamDb.dat file converter

[zimri-leisher]

F´ Version	3.5.1
Affected Component	PrmDb

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Feature Description

There should be a converter script which allows you to write paramdb files in human-readable form, e.g. json.

Rationale

We want to be able to set initial values of parameters based on a config file, not necessarily based on the .fpp files, which are set at compile time.

Potentially, also add a command in the PrmDb to reload the database. This would probably involve some autocoder work, so out of the scope of this ticket.

Potentially, also add an option to generate a sequence of commands instead of a dat file.
Potentially, also add an option to implicitly write defaults.
Potentially, also add an option to generate a "default" json file from the dictionary.

[zimri-leisher]

@LeStarch please assign to me

[zimri-leisher]

Impl note: should be under a fprime-params sub command

[zimri-leisher]

I know I said it would take me a while, but I had a bit of time to do it early, so I made a PR for this: nasa/fprime-gds#187
@LeStarch @timcanham