feat(ct-metrics): add initial conntrack metrics for Prometheus

[SRodi]

Description

Create initial metrics for conntrack:

• packets_count_per_connection [gauge] see example below
• bytes_count_per_connection [gauge]
• connections_count [count] WIP

Related Issue

#806

Checklist

• I have read the contributing documentation.
• I signed and signed-off the commits (git commit -S -s ...). See this documentation on signing commits.
• I have correctly attributed the author(s) of the code.
• I have tested the changes locally.
• I have followed the project's style guidelines.
• I have updated the documentation, if necessary.
• I have added tests, if applicable.

Screenshots (if applicable) or Testing Completed

This example shows a long-lived TCP connection between client src_ip="10.244.0..230 and server 10.244.1.85

This example shows the bytes_count_per_connection where dst_ip=10.244.0.113 which is the pod IP for metrics-server on one of the cluster nodes.

(WIP) Here is some initial work on Hubble metrics

Considerations

The number of time series increases overtime based on number of new connections in the cluster - the count of time series is the same for both packets_count_per_connection and bytes_count_per_connection metrics since both use the same labels.

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Please refer to the CONTRIBUTING.md file for more information on how to contribute to this project.

[MikeZappa87]

Did we think though around scalability, performance and stability when adding these metrics? Do we have any concerns? Do we have numbers to back this up?

[vakalapa]

Can you find a way to integrate these into Hubble metrics as well ?

[SRodi]

still WIP, but some initial work is done, see this screenshot