Add DNS provider for hosting.nl

[ldez]

• add 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 in your PR)

  make build
  rm -rf .lego
  
  HOSTINGNL_API_KEY="xxxxxxxxxxxxxxxxxxxxx" \
  ./dist/lego -m your@email.com --dns hostingnl -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 @arnovdk, can you run the command (with your domain, email, and credentials)?

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/hostingnl

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

   HOSTINGNL_API_KEY="xxxxxxxxxxxxxxxxxxxxx" \
   ./dist/lego -m your@email.com --dns hostingnl -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

Closes #1598