[feature] Added support for ZeroTier to the OpenWRT backend #207

[Aryamanz29]

Depends on:

• [x] https://github.com/openwisp/netjsonconfig/pull/272
• [x] https://github.com/openwisp/netjsonconfig/pull/278

Prerequisites:

1. Install Zerotier

2. Install Ztncui - Web Interface

3. Get your Zerotier Service API token sudo cat /var/lib/zerotier-one/authtoken.secret

Tested with openwisp-controller

• Prototype Branch: https://github.com/openwisp/openwisp-controller/tree/zerotier-prototype

https://github.com/openwisp/netjsonconfig/assets/56113566/886f0a65-8263-499e-ba33-7185f29b63fd

Closes #207

[coveralls]

coverage: 98.742% (+0.03%) from 98.711% when pulling db1a2161ce5844418065febe47d2f63751fdd196 on issue-207/add-zerotier-to-openwrt-backend into 3f14cae63c8ca12e8e792c73d17f9ff55c5837ed on gsoc23.