Create OAuth2Client recipe

[porcellus]

This should be a stripped down version of the ThirdParty recipe.

• It should have separate paths (do not overlap with ThirdParty)
• It only supports a single provider
• Remove config options & inputs that we do not need because of the single provider thing
• The only provider it supports is what we expose in the OAuth2 recipe (so the config should default to that)
  • We will want to enforce that the only thing supported (this is likely going to be a prefix check on the clientId)

[anku255]

Done in https://github.com/supertokens/supertokens-node/pull/877