Tags and host

[ChristopheSchmitz]

A few things in this PR:

• I think the cluster-id / instaclustr username / instaclustr password should not be in the bracket [ ]. Didn't work for me
• I added a custom tag list to be set at the configuration level
• Instead of creating one metric name per (public_ip, cassandra-metric) combination, I think we should report the metric using the cassandra-metric-name. Then we can slice with the extra tags that are now automatically created in the code, based on the rest api json we get.

[ChristopheSchmitz]

Probably need to be tested from a mac