[Feature] Allow overriding the title field of a type

[mstade]

Problem description

Currently you can use the docs field in a Fern type to set the description field in the generated OpenAPI spec, however there's no way to set the title field of the generated schema. Instead, it defaults to be the same as the type name.

Why would it be useful?

Being able to specify the title of a type adds another level of human readable documentation, in addition to the very useful docs field.

Describe the solution (optional)

I propose adding title as a field for any type, and that it follows the same semantics as the title field in the relevant JSON Schema spec, that is:

6.1. "title" and "description"
The value of both of these keywords MUST be a string.
Both of these keywords can be used to decorate a user interface with
information about the data produced by this user interface. A title
will preferrably be short, whereas a description will provide
explanation about the purpose of the instance described by this
schema.

Additional context

n/a