enh: subdomain addition + domain addition in app install

[Axolotle]

The problem

• sometimes you just want to add a subdomain, being able to just enter the subpath with your already added domain is less error prone.
• in AppInstall view you are sometimes required to add a specific subdomain for an app, having to return to DomainAdd to setup said new domain then run the diagnosis or force install a Let's Encrypt certificate is tedious.

Solution

• add subdomain option to DomainForm with ability to auto install the Let's encrypt certificate if a wildcard is detected in DNS records
• add ability to add a domain/subdomain directly in the AppInstall view in the domain field, as a modal, with auto select of the newly added domain.

PR Status

could'nt test the letsencrypt install properly (can't install certs on my setup idk why)

Requires: YunoHost/yunohost#1936
Fix: YunoHost/issues#1634

Preview

[selfhoster1312]

I don't understand why/how this is done on client side. In my opinion, it should be part of the app install route that you can specify a subdomain that does not exist that would be instantiated with a LetsEncrypt certificate. Whether this should be enabled by an additional flag/checkbox or be automatic i have no idea.

But doing it on the client side does not for example allow to do it from the CLI. Something like: yunohost app install -d my_sub.domain.tld my_app or yunohost app install --subdomain my_sub.domain.tld my_app or yunohost app install --new-subdomain -d my_sub.domain.tld.

Client side logic should only be for form validation and UX, and not for server configuration logic, otherwise review/maintenance becomes 10x more complex.

[alexAubin]

Having an entire set of argument for domain creation during the app install doesn't seem right ... CLI / API routes should be about somewhat ~atomic operations and there already are routes about adding a new domain ... The point of this PR is to

• a) somewhat formalize in terms of UI the procedure of "adding a subdomain" which currently ain't really clear (because people legitimately don't necessarily realize / understand that "adding a domain" can be used to add a subdomain),
• b) automatically add the Lets Encrypt cert to reduce the number of clicks (because the current workflow also require to visit the diagnostic etc)
• c) be able to add a domain from a quick modal that you can open from the app install form