feat: add refresh_oauth_token() API

[Verdgil]

request for access_token is exported to new method

[casbin-bot]

@seriouszyx @ComradeProgrammer @Resulte please review

[Verdgil]

@hsluoyz i fixed all comments

[hsluoyz]

@Verdgil if you are adding new API, add it to casdoor-go-sdk first

[Verdgil]

@Verdgil if you are adding new API, add it to casdoor-go-sdk first

I cann't append it to Go sdk, because i don't know go that much

But in go sdk, as i see, yours has refresh token api

[hsluoyz]

@Verdgil see: https://github.com/casdoor/casdoor-python-sdk/pull/32#discussion_r1041734446

[Verdgil]

@hsluoyz I did it

[hsluoyz]

@Verdgil also add this new API to README.md

[Verdgil]

@Verdgil also add this new API to README.md

I appended this, your whant docs in another place?

[github-actions[bot]]

:tada: This PR is included in version 1.4.0 :tada:

The release is available on:

• v1.4.0
• GitHub release

Your semantic-release bot :package::rocket: