Add support for refreshing access tokens

[akshgpt7]

Currently, the response_type parameter is set by default to token. This means we can't refresh the access token obtained. To refresh access tokens, access_type=offline has to be additionally passed while making the oauth request, which does not work with response_type=token. Instead, response_type must be set to code.

It is desired that if the user enters the refresh token (if they have it), youtube-deno handles the refresh flow and generates the new access token internally.

To achieve this:

• Remove the default value of response_type from here and let the user enter it as a required parameter.
• Change the second argument of the YouTube class to an object type, which can take three types of values: {access_token: "some-token"}, {refresh_token: "some-token"}, or {auth_code: "some-code"}.
• If the access_token is directly passed, store it to the this.token class variable. Else if refresh_token is passed, trigger the refresh flow and the returned access token is stored in this.token. If auth_code is passed, exchange it for access_token and store it in this.token.