[ docs ] Metrics paragraph should mention OpenTelemetry

[yonas]

PR https://github.com/sozu-proxy/sozu/pull/1176 didn't include an update for sozu.io's frontpage:

Metrics

Metrics work like the logger, accessible from anywhere with macros and TLS. We support two ‘drains’: one that sends the metrics on the networks with a statsd compatible protocol, and one aggregating metrics locally, to be queried through the configuration socket.

This paragraph should mention OpenTelemetry.

[FlorentinDUBOIS]

Thank you for the report, I will update the website!

[yonas]

I found a copy in https://github.com/sozu-proxy/sozu/blob/main/doc%2Farchitecture.md