Updating documentation around the opentelemetry endpoint for metrics and
the "How to use OpenTelemetry metrics with VictoriaMetrics" guide so
that it shows not only how to directly write but also how to write to
the otel collector and view metrics in vmui.
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Signed-off-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>
Co-authored-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>
