include $schema version declaration in json schema exports

[gwennlbh]

Hi!

I noticed that the exported JSON Schema object does not include the $schema key, which declares the meta schema (and thus declares which version of JSON schema this is intended to be used with)

I used the latest version and hardcoded the string, it might be worth factoring out

In order to only add the $schema key at the top-level, I added a new .toJsonSchemaNoVersion method that does what .toJsonSchema did before

I wonder if the usages of .toJsonSchema could be replaced with .innerToJsonSchema so we don't have to add a new method?

I also tried putting the version inclusion as an optional argument to .toJsonSchema, but it seems like my typescript powers are not strong enough yet, I get a type error at the Object.assign call when doing

toJsonSchema<IncludeVersion extends boolean | undefined>(includeVersion?: IncludeVersion): IncludeVersion extends true ? FinalJsonSchema : JsonSchema

Thanks a lot for this project, it's really impressive and the DX is great :3

[gwennlbh]

It might be worth using draft-07 instead, VS Code warns me on unsupported features (namely "$dynamicRef" i believe) for newer versions

[ssalbdivad]

Hey thanks so much for this PR it was very useful!

I'm updating the toJsonSchema API to be more flexible. The approach will be a bit different so I'm going to close this, but I referred it throughout the process and it was useful ❤️