Request TLS certificate for Tailnet name

[lmagyar]

Replaces PR #89

Fixes #62

PR #130, #131, #132 and #133 precedes this PR

Update: PR #137 I think is a better solution to the #62 issue, because #137 doesn't need any manual configuration and also provides a built-in proxy for the https traffic (we don't need to refresh the certificates, this is all done by tailscale automatically).

Proposed Changes

Request TLS certificate for Tailnet name

This is based on #89, but

• the Configuration option is certificate_tailnet_name (not domain_alias), it is more logical, it is analog to the tailscale cert <machine-name>.<tailnet-name>.ts.net command
• it creates the /ssl/tailscale directory before fetching the cert
• uses --statedir=/data instead of --state=/data/tailscaled.state, see Tailscale.sh: use --statedir instead of --state tailscale/tailscale-qpkg#64
• fetch certificate on start and only within 1 week before expiration
• modified the daemon finish script to the usual script, I know new add-ons have better, it can be bumped later with other scripts

[lmagyar]

I've renamed the config option (again), from cert_domain to certificate_tailnet_name, because it was misleading, <cert-domain>=<machine-name>.<tailnet-name>.ts.net

[lmagyar]

I'm closing this PR in favor of #137, because that provides more functionality with no configuration.