Add check_curl to ITL

[RincewindsHat]

Adding check_curl from Monitoring Plugins to the ITL

[RincewindsHat]

Added some documentation

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Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Lorenz Kästle. This is most likely caused by a git client misconfiguration; please make sure to:

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[cla-bot[bot]]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Lorenz Kästle. This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email [email protected]
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[hydrapolic]

This would be nice as check_http is going to be removed https://github.com/monitoring-plugins/monitoring-plugins/pull/1806