[OAS] Add a 'allowReserved' handling for query parameters into generation templates

RFC 3986 defines a set of reserved characters :/?#[]@!$&'()*+,;= that are used as URI component delimiters. When these characters need to be used literally in a query parameter value, they are usually percent-encoded. For example, / is encoded as %2F (or %2f), so that the parameter value quotes/h2g2.txt would be sent as

GET /file?path=quotes%2Fh2g2.txt

If you want a query parameter that is not percent-encoded, add allowReserved: true to the parameter definition:

parameters:
  - in: query
    name: path
    required: true
    schema:
      type: string
    allowReserved: true # <-----

In this case, the parameter value would be sent like so:

GET /file?path=quotes/h2g2.txt

Actual result:

There is no checks for 'allowReserved' value in the generator's code.

Expected result:

Add  the check in *.mustache files , that reads 'allowReserved' value and applies/or not applies toPercentEncoding().

More info:

See https://swagger.io/docs/specification/v3_0/describing-parameters/