Add DNS provider for ManageEngine CloudDNS

[ldez]

• adds a description to your PR
• have a homogeneous design with the other providers
• 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)

  make build
  rm -rf .lego
  
  MANAGEENGINE_CLIENT_ID="xxx" \
  MANAGEENGINE_CLIENT_SECRET="yyy" \
  ./dist/lego -m [email protected] --dns manageengine -d *.example.com -d example.com -s https://acme-staging-v02.api.letsencrypt.org/directory run

  Note the wildcard domain is important.
• pass the linter
• do go mod tidy

Ping @dgarner-cg, can you run the command (with your domain, email, credentials, etc.)?

-> #2365 (comment)

Closes #1933

How to test this PR?

1. You need Go
2. Checkout the PR:

   git clone https://github.com/ldez/lego.git
   cd lego
   git checkout feat/manageengine

3. Compile lego:
   • if you have make: make build
   • if you don't make make: go build -o dist/lego ./cmd/lego
4. Run the following command with your information (email, domain, credentials):

   MANAGEENGINE_CLIENT_ID="xxx" \
   MANAGEENGINE_CLIENT_SECRET="yyy" \
   ./dist/lego -m [email protected] --dns manageengine -d *.example.com -d example.com -s https://acme-staging-v02.api.letsencrypt.org/directory run

   The wildcard domain is important
5. Before each run of the command, you should clean your local environment:

   rm -rf .lego

[dgarner-cg]

Great, I'm primary support this weekend so depending on how busy we are, I'll be stuck in front of a computer, hopefully nothing going on, if so, maybe then; otherwise, the following week/weekend.
Or you can email me your preferred contact via the email in our chain with Manage Engine, which ever you prefer.

I did send something now, will do more shortly. :)

[dgarner-cg]

Changes have successfully allowed ACME verification through Manage Engine's CloudDNS provider.

[dgarner-cg]

@ldez
Ohh, forgot .. in our excitement, forgot..
Are you going to submit a new PR to remove the verbose logging and whatnot added to debug API issue?

[ldez]

I have already removed the debug logs from this PR.

There is some debug information behind an env var.
I added the additional logs during the development of this PR to help understand the API.
Now, I understand the API (and even the API doc 😸)

[dmke]

LGTM