[oidc-middleware] Add oidcClientOptions

[denysoblohin-okta]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] The commit message follows our guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [x] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Adding Tests
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation changes
• [ ] Other... Please describe:

What is the current behavior?

Customer reports then default authorization for /token endpoint (client_secret_basic) doesn't work for some reason (related to configuration of his network probably) but client_secret_post works.

Issue Number: OKTA-379204

What is the new behavior?

Developer can pass custom options to OpenId Client constructor

Should resolve issue https://github.com/okta/samples-nodejs-express-4/issues/105 by adding

    oidcClientOptions: {
      token_endpoint_auth_method: 'client_secret_post',
    }

in options for ExpressOIDC here: https://github.com/okta/samples-nodejs-express-4/blob/master/common/sample-web-server.js#L31

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

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