Every other package in this repository is installed
with yarn; yhub-server was the only one on npm,
with its own package-lock.json.
To ensure consistency it now uses yarn like the rest
of the project.
package-lock.json is replaced by yarn.lock, a packageManager
field is added, and the Dockerfile, CI workflow, Makefile,
helm init-db job and the documentation move from
`npm ci` / `npm run init-db` to
`yarn install --frozen-lockfile` / `yarn init-db`.
The new infra we have must be configured in the helm chart. This commit
all the missing templates to deploy yhub, it also automate the creation
of the private keys needed by all services.
