Support exporting OpenTelemetry Exponential Histograms from Pixie

[philkuz]

Is your feature request related to a problem? Please describe.
Exponential Histograms are a flexible metric type meant to represent distributions. We currently support a similar metric type, Summary. However, Summary is currently in legacy mode with OpenTelemetry - largely because there is no natural way to aggregate summaries together.
Caveat:
ExponentialHistogram is currently in experimental stage which means it can change between API versions, but there is a push to stabilize it: open-telemetry/opentelemetry-specification#2832.

Describe the solution you'd like
syntax:

    px.otel.metric.ExponentialHist(
      name="dns.latency",
      description="DNS latency",
      value=df.hist_latency,
    ),

In this case we would probably want a UDA that creates the histogram. Defining a histogram manually
would be extremely tedious for an end-user.

Having histograms would also solve a burning need we have to properly merge percentile values together.

Describe alternatives you've considered
We could also go with normal Histogram types instead which are currently stable, but are far less flexible for our use-case given that the data we see might vary wildly in scales.
Additional context
ExponentialHistogram docs: https://opentelemetry.io/docs/reference/specification/metrics/data-model/#exponentialhistogram
OTel-proto PR for ExponentialHistogram: open-telemetry/opentelemetry-proto#322