Allow custom path when querying the core

[rishabhpoddar]

If someone is hosting the core on a domain that is shared by other resources (like webserver or API server), then they would want to query the core via its own path, like example.com/supertokens.

This would entail that the backend SDK should accept a basePath and add that to the core's domain when querying it.

It would also imply that they would have to add a reverse proxy between the backend SDK and the core that would strip away this basePath - unless we can configure the core to have this base path as well.

TODO:

• core
• nodejs
• golang
• python
• docker config
• docs