Servantify cargohold and add federationDomain option

[pcapriotti]

This converts the public API to Servant, removes the dependency on wai-routing, and also introduces a mandatory federationDomain configuration option.

Tracked by https://wearezeta.atlassian.net/browse/SQCORE-1174.

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• If HTTP endpoint paths have been added or renamed, the endpoint / config-flag checklist (see Wire-employee only backend wiki page) has been followed.
• If a cassandra schema migration has been added, I ran make git-add-cassandra-schema to update the cassandra schema documentation.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.
  • If public end-points have been changed or added: does nginz need un upgrade?
  • If internal end-points have been added or changed: which services have to be deployed in a specific order?

[jschaul]

Approving the federationDomain setting option in its various incantations. The rest I just skimmed.

[fisx]

Could you rebase this so it doesn't contain other PRs any more?

[fisx]

this doesn't match the title of the PR.

[pcapriotti]

True, but it would be somewhat painful to split this into two PR, since the ZAuth servant combinators have integration with the Qualified stuff that needs knowledge of the federation domain, which we'll need in cargohold later anyway. It would just be more pointless work to do this in two steps.

Can I just expand the PR description to include this?

[pcapriotti]

I updated the title and description. Ok to merge?

[pcapriotti]

Could you rebase this so it doesn't contain other PRs any more?

Done. The unrelated schema changes are now gone.