[dnsapi] add MVMNET dns api

[marchrius]

This PR adds support for MVMNET DNS API https://mvmnet.com with docs at https://api.mvmnet.com/api/1.0/documentation/.

Features

• Add TXT records for ACME challenge
• Remove TXT records after validation

Testing

• Tested with staging and production environment
• Tested certificate issuance
• Tested automatic renewal

Usage

export MVMNET_ID="your_application_id"
export MVMNET_KEY="your_application_key"
export MVMNET_SEED="your_application_seed"

acme.sh --issue -d example.com --dns dns_mvmnet

The environment variables as case sensitive also in the value itself, keep attention to this.

Warnings

I cannot launch the test flow on GitHub because the API documentation and the API itself are behind a firewall set by provider. You need to contact the support through the ticket system at http://supporto.mvmnet.com/ and request for an IP assignation.

[github-actions]

Welcome
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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.