Add virtualname DNS API plugin

[aalmenar]

This PR adds a DNS API plugin for Virtualname.net API

• Supports ACME DNS-01 TXT record management (adds/removes _acme-challenge TXT records)
• Uses the official REST API (Swagger): https://developers.virtualname.net
• Saves credentials to account.conf for non-interactive renewals (per DNS-API-Dev-Guide)

Configuration:

VIRTUALNAME_API_TOKEN

[github-actions]

Welcome
READ ME !!!!!
Read me !!!!!!
First thing: don't send PR to the master branch, please send to the dev branch instead.
Please read the DNS API Dev Guide.
You MUST pass the DNS-API-Test.
Then reply on this message, otherwise, your code will not be reviewed or merged.
Please also make sure to add/update the usage here: https://github.com/acmesh-official/acme.sh/wiki/dnsapi2
注意: 必须通过了 DNS-API-Test 才会被 review. 无论是修改, 还是新加的 dns api, 都必须确保通过这个测试.

[neilpang]

https://github.com/acmesh-official/acme.sh/wiki/DNS-API-Test