omniauth v2 support

[ssaveleva-workato]

TL;DR

added some options to support omniauth v2.
changes are compatible with omniauth v1.9.

Changes detail

there were 2 problems:

1. Wrike requires client_id and client_secret to be passed as parameters when receiving a token https://developers.wrike.com/oauth-20-authorization/

POST https://login.wrike.com/oauth2/token
//Parameters:
client_id=<client_id>
client_secret=<client_secret>
grant_type=authorization_code
code=<authorization_code>

but in oauth2 v2 the headers are used by default.
auth_scheme: :request_body fixes this.

2. redirect_uri is passed with parameters and it doesn't work. Here's a similar issue: When calling /auth/:identity/callback.json , request.env["omniauth.auth"] is nil omniauth/omniauth#618

the fix is to redefine callback_url not to add query_string by default. as it was made in omniauth-google-oauth2: https://github.com/zquestz/omniauth-google-oauth2/blob/v1.1.1/lib/omniauth/strategies/google_oauth2.rb#L116