Limiter extension API interfaces and implementation helpers (**draft 6**)

[jmacd]

Description

Improves on the previous drafts:

Removes the SaturationChecker interface with only MustDeny(). This feature was a mistake, the concept of saturation is not required. The memorylimiterextension is modeled as a rate-limiter extension, instead. This reduces API surface area significantly.

Adds consumerlimiter package with NewLimitedFactory() for constructing receivers with pipelines that automatically apply limiters, configured by embedding the consumerlimiter.LimiterConfig, see the README.

Documents a proposed collector extension interface style called "Functional Composition". This is a draft, see docs/rfcs/functional-composition-pattern.md. If we like this, I'll put it in a separate PR.

Middleware config syntax proposal. A number of people have stumbled over the current syntax, which has the configmiggleware.Config item as a struct containing a single Id field. Instead, it could be a non-struct type (component.ID). See the open questions section in README.md.

Follows drafts
1: #12558
2: #12633
3: #12700
4: #12953
5: #13051

Link to tracking issue

Part of #7441
Part of #9591
Part of #12603
Part of #13228

Testing

N/A This will be broken into smaller PRs with tests.

Documentation

Documentation has been updated with new open questions.

[jmacd]

Closed in favor of #13265