Add support to formParameters

[jamillosantos]

This PR implements the formParameters option on the request as specified at https://wiremock.org/docs/request-matching/#request-with-form-parameters

When dealing with application/x-www-form-urlencoded POST requests, the formParameters option makes the life of developer easier for building assertions on requests.

Example:

Client.StubFor(
	wiremock.Post(wiremock.URLPathEqualTo("/url")).
		WithFormParameter("parameter", wiremock.EqualTo("value")).
		WillReturnResponse(...),
)

References

• https://wiremock.org/docs/request-matching/#request-with-form-parameters

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