otlptext support for ExponentialHistogram

[jmacd]

Describe the bug
The otlptext package does not recognize ExponentialHistogram data types.

Steps to reproduce
Demonstrated in open-telemetry/opentelemetry-collector-contrib#6666 using a logging exporter and a statsd receiver configured to produce exponential histograms.

What did you expect to see?
The data type should print its buckets in a human readable way.

What did you see instead?
Nothing prints.

What version did you use?
60823e2

What config did you use?

receivers:
  statsd:
    endpoint: :8127
    aggregation_interval: 10s
    is_monotonic_counter: true
    timer_histogram_mapping:
    - statsd_type: histogram
      observer_type: histogram
      histogram:
        max_size: 16
    - statsd_type: timing
      observer_type: histogram
      histogram:
        max_size: 128

exporters:
  logging:
    loglevel: debug
   
service:
  pipelines:
    metrics:
      receivers: [statsd]
      exporters: [logging]