chore: add support for oauth

[tiwarishubham635]

Fixes

This PR adds support for accessing Twilio APIs using OAuth2 as well. It adds the following classes:

1. Token Managers to fetch access token
2. AuthStrategy to use tokens and create authString
3. Credential Providers to choose different auth strategy, be it - Basic Auth, OAuth or NoAuth (Limited use)
4. Modifications to Client to accomodate new changes without breaking previous flow

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[tiwarishubham635]

Add tests for validating OAuth based api calls

[sonarcloud]

Quality Gate failed

Failed conditions
26.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud