Change preview hostname construction, enabling wildcard TLS certificates

[axisofentropy]

We want to use "wildcard" TLS certificates to stop relying upon third-party certificate authorities for each new deployment. This should increase reliability and sometimes speed of new deployments. The easiest way to implement this is to use a single wildcard TLS certificate for all deployments. This requires that all deployments be subdomains of a single domain.

For example, a certificate for *.example.com will match foo.example.com but will not match foo.bar.example.com. As Wikipedia says:

[...] the wildcard only covers one level of subdomains (the asterisk doesn't match full stops.)

Maybe we can easily change how our app generates hostnames to only use a single level of subdomain. This could be as easy as replacing . with -. Other tickets will describe changes to our controller and infrastructure.

This is a feature we want to become the most common case, so I don't think we need a feature "gate" like an environment variable.

Be mindful of RFC 1035 which specifies "Labels must be 63 characters or less."! https://datatracker.ietf.org/doc/html/rfc1035

[moklidia]

For QA:

• The hostname construction is changed so it consists of a single subdomain
• If the subdomain length is bigger than 63 characters it gets cut

[NealArw]

TESTED - OK

[NealArw]

TESTED on prod - OK