feat: Sidekiq metrics / metrics integration draft

[zvkemp]

Still todo:

• test that metrics aren't included if the option is disabled
• move a bunch of logic into Instrumentation::Base or an appropriate mixin
• standardize the logic gating on presence/absence of the metrics-api gem
• should metrics-api be unconditionally required? I.e does the presence of metrics-api in the bundle mean it should be considered active?
• test the client middleware
• any metrics on the other patch modules?
• Once the logic has been moved to its appropriate home, this PR should be split into at least two parts; 1) for generic metrics support on Instrumentation::Base and 2) concrete metrics on sidekiq

blockers

• opentelemetry-metrics-api and opentelemetry-metrics-sdk are not in sync (metrics-sdk is newer, and includes methods that aren't implemented by the rubygems version of metrics-api). In tests, I am bundling from github for both of them.
• Semantic conventions for metrics are not present in the ruby lib
• messaging.queue.latency should be proposed to semconv
• resolve question of how to time metrics that correspond to a span — it seems like in most cases a collector should be able to synthesize histograms or counters for anything with a span; unclear why semconv demands some required metrics that also have spans.

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