Allow force refreshing of the access token

[ghost]

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Description

The purpose of this pr is to allow the access token to be refreshed manually

Provide details that support your chosen implementation, including: breaking changes, alternatives considered, changes to the API, etc.
Changes are to AccessTokenRequest interface to allow the option refresh which is not required.
and inside of getAccessToken() where it would check if the token was expired and there is a refresh token it now also checks
(session.refreshToken && accessTokenRequest && accessTokenRequest.refresh

How it can be used is getAccessToken({refresh:true})

References

Include any links supporting this change such as a:

• Allow manual refresh for access token #136

Testing

Describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and/or integration testing, tests should be added for new functionality and existing tests should complete without errors.
Added a new test for this outcome next with the same code with a change to the time that is used to test the expired access token

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[sandrinodimattia]

Thank you! This is now available in v0.16 👍