[http] Add optional TLS client cert authentication

[riton]

Checklist

• [x] unit and/or integration tests are included (if applicable)
• [x] documentation is changed or added (if applicable)

Description of change

This P.R adds ability to authenticate using a client certificate in http test suites.

Example:

---
http:
  https://cc.in2p3.fr/server/that/requires/tls-client-authn:
    status: 200
    client-cert-auth:
      cert: '/path/to/certificate.pem'
      private-key: '/path/to/private-key.pem'
    [...]

[riton]

I've just realized that my editor ( V.S Code ) has updated the Table Of Content of the manual.md file behind my back.

If this is a problem for you, let me know and I'll revert those automatic changes.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[riton]

Not interested in this feature :innocent: ?

[ripienaar]

Not interested in this feature 😇 ?

The author is in a position where he can't reply atm to these things, it does not mean there's no interest.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[aelsabbahy]

Thank you, this has been merged (with minor changes) and will be in the next goss release.