📖docs: improve MaxConcurrentReconciles documentation (#3521)

* docs: improve MaxConcurrentReconciles documentation

Add detailed Go doc comments for MaxConcurrentReconciles explaining:

- The option controls the number of worker goroutines processing items
  from the controller's work queue
- Different queue items may be reconciled concurrently, but the same
  item is never processed by multiple workers at the same time
- If the same item is added again while being processed, it is marked
  dirty and requeued after the current reconciliation finishes
- Increasing concurrency can improve throughput but may increase load
  on the API server and external systems; QPS/Burst settings should be
  considered
- Manager-level (config.Controller) and GroupKind-level configuration
  are also available; per-controller values take precedence

* Update pkg/controller/controller.go

Co-authored-by: Alvaro Aleman <alvaroaleman@users.noreply.github.com>

* docs: simplify MaxConcurrentReconciles comment in TypedOptions

* Update pkg/controller/controller.go

Co-authored-by: Alvaro Aleman <alvaroaleman@users.noreply.github.com>

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Co-authored-by: Alvaro Aleman <alvaroaleman@users.noreply.github.com>