Adding websocket upgrade support

[taiidani]

Taking inspiration from https://github.com/http-party/http-server/pull/637 and attempting to address the changes requested from the PR review

Adding a handler for an "upgrade" request so that the proxy properly manages the connection to the downstream.

Relevant issues

Fixes #142.

Contributor checklist

• [ ] Provide tests for the changes (unless documentation-only)
• [x] Documented any new features, CLI switches, etc. (if applicable)
  • [x] Server --help output
  • [x] README.md
  • [x] doc/http-server.1 (use the same format as other entries)
• [x] The pull request is being made against the master branch

Maintainer checklist

• [ ] Assign a version triage tag
• [ ] Approve tests if applicable

[github-actions[bot]]

This pull request has been inactive for 360 days