[chore] Rename disabled queue to waiting queue, implement size limit

[bogdandrutu]

No need yet for changelog entry because this is not enabled, pending the new queue-batch config.

[codecov]

Codecov Report

Attention: Patch coverage is 86.36364% with 9 lines in your changes missing coverage. Please review.

Project coverage is 91.61%. Comparing base (f09dad4) to head (5ac90ac).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
exporter/exporterqueue/waiting_queue.go	85.93%	6 Missing and 3 partials ⚠️

❌ Your patch check has failed because the patch coverage (86.36%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12652      +/-   ##
==========================================
- Coverage   91.63%   91.61%   -0.03%     
==========================================
  Files         479      479              
  Lines       26423    26452      +29     
==========================================
+ Hits        24214    24234      +20     
- Misses       1749     1755       +6     
- Partials      460      463       +3     

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[jmacd]

If this were only the renaming, I'd agree it's a chore not needing a changelog. But the new condition variable... I would add a changelog about the size limit. If a user is using queue-disabled today, does the condition variable mean slightly more synchronization cost? I'm trying to imagine a user who might like to read that changelog.

[jmacd]

Suggested change

	// Ignore empty requests.
	// Ignore empty requests, see https://github.com/open-telemetry/opentelemetry-proto/blob/main/docs/specification.md#empty-telemetry-envelopes

[bogdandrutu]

If this were only the renaming, I'd agree it's a chore not needing a changelog. But the new condition variable... I would add a changelog about the size limit. If a user is using queue-disabled today, does the condition variable mean slightly more synchronization cost? I'm trying to imagine a user who might like to read that changelog.

Because the "size limit" is max int64, it will never get to the Wait() path, and then it means the Signal path if a if check, see from https://github.com/open-telemetry/opentelemetry-collector/blob/main/exporter/exporterqueue/cond.go:

// Signal wakes one goroutine waiting on c, if there is any.
// It requires for the caller to hold c.L during the call.
func (c *cond) Signal() {
	if c.waiting == 0 { // Nobody waits ever here.
		return
	}
	c.waiting--
	c.ch <- struct{}{}
}