Feat: Support x-scapi-internal (@W-18760261@)

[joeluong-sfcc]

NOTE: I will fix the CI in a separate PR for ease of review

This PR refactors the api template and pulls out certain parts into mustache partials. This PR also adds support for the x-scapi-internal custom vendor extension. Whenever an operation is tagged as x-scapi-internal: true, we'll hide that operation from being generated in the SDK

Example:

    get:
      x-scapi-internal: true
      description: ...
      operationId: getProduct

There's unfortunately lots of duplicated code as we have to handle 2 cases

1. The operation has vendor extensions and x-scapi-internal is present
2. The operation has no vendor extensions

{{#vendorExtensions}}
{{^x-scapi-internal}}
// Render content for operations that have vendor extensions but NOT x-scapi-internal
{{/x-scapi-internal}}
{{/vendorExtensions}}
{{^vendorExtensions}}
// Render content for operations that have no vendor extensions at all
{{/vendorExtensions}}

To test, you can update apis/products-oas/shopper-products-oas-1.0.36/shopper-products-oas-v1-internal.yaml and add x-scapi-internal to the getProduct/getProducts endpoints, and another custom vendor extension for getCategories:

paths:
  /organizations/{organizationId}/products:
    get:
      x-scapi-internal: true
      operationId: getProducts
  /organizations/{organizationId}/products/{id}:
    get:
      x-scapi-internal: true
      operationId: getProduct
  /organizations/{organizationId}/categories:
    get:
      x-sdk-test: true
      operationId: getCategories

[vcua-mobify]

I've verified that adding x-scapi-internal will result in the operation it's tagged with to not be included in the generated sdk.