Add CAIDA Ark monitor crawler

[m-appel]

Description

Adds information about CAIDA Ark monitors and links them to their country, AS, and geocoordinates. Also adds a new node type ArkMonitor that is similar to the existing AtlasProbe type since it contains multiple properties as well.

Motivation and Context

We have RIPE Atlas probes so having CAIDA Ark monitors as well only makes sense (and was requested by some users). This enables queries for Ark monitors in certain ASes or countries, which would require looking at the table on their website otherwise.

How Has This Been Tested?

Ran the crawler.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[romain-fontugne]

Looks good to me. Just the introductory sentence in the acknowledgement is not stating the write number of datasets (wrong even before the PR :D )