Add an option to disable converting path params into camelCase

If I have a snake_case path param in original schema like

```yaml
/some/{path_param}/:
...
parameters:
- name: path_param
in: path
required: true
type: string
```

then it'll be converted into camelCase in generated route (using `generateRouteTypes: true`):

```ts
'/some/{path_param}/': {
get: {
params: {
pathParam: number;
};
...
};
}
```

I guess I found this place and I see that this behavior is hard-coded:
https://github.com/acacode/swagger-typescript-api/blob/2b6db2346028fe6fb1f311bf5b1221a89837032e/src/schema-routes/schema-routes.js#L252

The problem is that in our project we don't want path params to be converted into camelCase. We expecting that they are stay as given by schema.

Would be nice to have an option for `generateApi` for disabling this converting. Something like

```ts
return generateApi({
generateRouteTypes: true,
pathParamsInCamelCase: false, // true by default for example
});
```