[Java] Add support for Bearer Auth

Created by: davidwcarlson

Fix proposed for Issue OpenAPITools#457 Similar to Issue OpenAPITools#1446 for typescript, Issue OpenAPITools#1577 for python

Specs defined as follows currently generate HttpBasicAuth and send an Authorization: Basic [base64Encode(username + ":" + password)] header

    components:
      securitySchemes:
        bearer:
          type: http
          scheme: bearer

This change will generate code which uses a new HttpBearerAuth class, which will send an Authorization: [scheme] [accessToken] header.

This change is slightly larger and more impactful than reusing the OAuth when CodegenSecurity.bearerBearer is true, but it allows for scheme values other than bearer.

This fix was enabled by the recent commit of OpenAPITools@80ca67c

This PR is an alternative to PR OpenAPITools#1972

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc) Add a new Auth type for Bearer so that api specs using Bearer Authentication https://swagger.io/docs/specification/authentication/bearer-authentication/ use the correct auth (was BasicAuth).

Copying the Java technical committee as this is a change targeted to Java. @bbdouglas @JFCote @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger