Add DNS provider for all-inkl

[ldez]

• have a homogeneous design with the other providers
• pass the linter
• do go mod tidy
• add tests (units)
• add tests ("live")
• add a provider descriptor
• generate CLI help, documentation, and readme.
• be able to do: (and put the output of this command to a comment)

$ rm -rf .lego
$ ALL_INKL_LOGIN=xxx ALL_INKL_PASSWORD=yyy ./dist/lego --email email@example.com --dns allinkl --domains lego.example.com --domains *.lego.example.com -s https://acme-staging-v02.api.letsencrypt.org/directory run
2021/06/30 18:19:57 No key found for account d594200b1d@firemailbox.club. Generating a P256 key.
2021/06/30 18:19:57 Saved key to /home/ldez/sources/go/src/github.com/go-acme/lego/.lego/accounts/acme-staging-v02.api.letsencrypt.org/d594200b1d@firemailbox.club/keys/d594200b1d@firemailbox.club.key
2021/06/30 18:19:58 Please review the TOS at https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf
Do you accept the TOS? Y/n
y
2021/06/30 18:19:59 [INFO] acme: Registering account for d594200b1d@firemailbox.club
!!!! HEADS UP !!!!

Your account credentials have been saved in your Let's Encrypt
configuration directory at "/home/ldez/sources/go/src/github.com/go-acme/lego/.lego/accounts".

You should make a secure backup of this folder now. This
configuration directory will also contain certificates and
private keys obtained from Let's Encrypt so making regular
backups of this folder is ideal.
2021/06/30 18:20:00 [INFO] [lego.example.com, *.lego.example.com] acme: Obtaining bundled SAN certificate
2021/06/30 18:20:00 [INFO] [*.lego.example.com] AuthURL: https://acme-staging-v02.api.letsencrypt.org/acme/authz-v3/78868798
2021/06/30 18:20:00 [INFO] [lego.example.com] AuthURL: https://acme-staging-v02.api.letsencrypt.org/acme/authz-v3/78868799
2021/06/30 18:20:00 [INFO] [*.lego.example.com] acme: use dns-01 solver
2021/06/30 18:20:00 [INFO] [lego.example.com] acme: Could not find solver for: tls-alpn-01
2021/06/30 18:20:00 [INFO] [lego.example.com] acme: Could not find solver for: http-01
2021/06/30 18:20:00 [INFO] [lego.example.com] acme: use dns-01 solver
2021/06/30 18:20:00 [INFO] [*.lego.example.com] acme: Preparing to solve DNS-01
2021/06/30 18:20:01 [INFO] [lego.example.com] acme: Preparing to solve DNS-01
2021/06/30 18:20:02 [INFO] [*.lego.example.com] acme: Trying to solve DNS-01
2021/06/30 18:20:02 [INFO] [*.lego.example.com] acme: Checking DNS record propagation using [192.168.1.1:53]
2021/06/30 18:20:04 [INFO] Wait for propagation [timeout: 1m0s, interval: 2s]
2021/06/30 18:20:04 [INFO] [*.lego.example.com] acme: Waiting for DNS record propagation.
2021/06/30 18:20:12 [INFO] [*.lego.example.com] The server validated our request
2021/06/30 18:20:12 [INFO] [lego.example.com] acme: Trying to solve DNS-01
2021/06/30 18:20:12 [INFO] [lego.example.com] acme: Checking DNS record propagation using [192.168.1.1:53]
2021/06/30 18:20:14 [INFO] Wait for propagation [timeout: 1m0s, interval: 2s]
2021/06/30 18:20:22 [INFO] [lego.example.com] The server validated our request
2021/06/30 18:20:22 [INFO] [*.lego.example.com] acme: Cleaning DNS-01 challenge
2021/06/30 18:20:25 [INFO] [lego.example.com] acme: Cleaning DNS-01 challenge
2021/06/30 18:20:26 [INFO] [lego.example.com, *.lego.example.com] acme: Validations succeeded; requesting certificates
2021/06/30 18:20:26 [INFO] [lego.example.com] Server responded with a certificate.

Closes #1328

[dmke]

LGTM!