feat: uses can overwrite def-0 logic

[Eomm]

Supersedes #4
Refs:

• References to "definitions"  fastify/fastify-swagger#337
• Schema added using fastify.addSchema is resulted as "def-#" in Swagger Models section fastify/fastify-swagger#286
• Swagger Docs generated do not show added schemas as models fastify/fastify-swagger#225
• Add support for $ref in header schemas fastify/fastify-swagger#432

TODO

• Testing withing fastify-swagger

[mikicho]

@Eomm why don't you use the $id property if exists?

[Eomm]

Because the $id is not an id as in relational database. It is a uri that must be resolved against other $ids.

So what the use need is a simple map id - value, but the spec doesn't define it like this