Enable event filtering in LiveView instrumentation

[marcdel]

Is your feature request related to a problem? Please describe.
LiveView can be very noisy, and the current implementation of opentelemetry_phoenix currently only supports enabled/disabled (I believe).

Describe the solution you'd like
I'm not sure the best general solution, presumably an allow and/or deny list for filtering these events.

Describe alternatives you've considered
My current solution, as suggested in the Elixir slack, is a custom sampler.

defmodule SpanNamesSampler do
  def setup(attributes) when is_map(attributes) do
    attributes
  end

  def setup(_), do: %{}

  def description(_), do: "Allows you to drop spans based on their name."

  def should_sample(_ctx, _trace_id, _links, span_name, _span_kind, _attributes, config_attributes) do
    spans_to_drop = Map.get(config_attributes, :spans_to_drop, [])

    if Enum.member?(spans_to_drop, span_name) do
      {:drop, [], []}
    else
      {:record_and_sample, [], []}
    end
  end
end

config :opentelemetry, sampler: {SpanNamesSampler, %{spans_to_drop: ["super-annoying-event-handler"]}}