Support article for per channel stats

[mattheworiordan]

A few customers have asked about per channel stats, something we do not support.

We should write an article that:

• Explains why we don't do this i.e. infrastructure cost of this for customers with very high cardinality of channels.
• Describe how to use popular channels functionality we're making available soon in our dashboards
• Tells them to get in touch if they need help or can explain their use case in more detail.

┆Issue is synchronized with this Jira Task by Unito

[mattheworiordan]

Mention that we may offer integrations with Datadog, and get in touch if they're interested