Fix prometheusreceiver TA/scrape_config validation logic

[Aneurysm9]

Description: Fixes faulty logic regarding requirement that either Prometheus scrape_configs or target allocator configuration be provided.

Testing: Tests are added that ensure valid combinations are accepted.

[bogdandrutu]

Though, I don't agree with the overall approach of forcing this PR before the refactoring PR that showed this problem just because the author blocked the other PR, I am ok approving since this fixes a problem.

[bogdandrutu]

I would suggest moving this to the validatePromConfig simplifies indentation.

[Aneurysm9]

That's where it was and you told me to move it.

[bogdandrutu]

I told to move the following code in the config.Validate

	if (promConfig == nil || len(promConfig.ScrapeConfigs) == 0) && cfg.TargetAllocator == nil {
		return errors.New("no Prometheus scrape_configs or target_allocator set")
	}

And in this comment I asked to move in the validatePromConfig

	if promConfig == nil {
		return nil
	}

[bogdandrutu]

Author ignored reviewer comments, please at least disagree with them, not just mark them as resolve like #30135 (comment)

[bogdandrutu]

I told to move the following code in the config.Validate

	if (promConfig == nil || len(promConfig.ScrapeConfigs) == 0) && cfg.TargetAllocator == nil {
		return errors.New("no Prometheus scrape_configs or target_allocator set")
	}

And in this comment I asked to move in the validatePromConfig

	if promConfig == nil {
		return nil
	}

[bogdandrutu]

PR forked and comments fixed in #30181.

[Aneurysm9]

@bogdandrutu I was on vacation when you took it upon yourself to fork this to make irrelevant changes. You approved the exact same code you later blocked. I took that to mean that the comments you made were not required to be addressed and they did not appear to me to be relevant or useful in light of the in-flight refactoring PR you have open. In the future if you expect that comments will lead to changes perhaps don't also indicate your approval.

[bogdandrutu]

@bogdandrutu I was on vacation when you took it upon yourself to fork this to make irrelevant changes.

I would kindly ask you to avoid calling changes asked by peers/reviewers as "irrelevant".

You approved the exact same code you later blocked.

I did approve the change with some comments, for me that means that I trust you will resolve the comments, but they are not significant to require a new review.

I took that to mean that the comments you made were not required to be addressed and they did not appear to me to be relevant or useful in light of the in-flight #29901 you have open. In the future if you expect that comments will lead to changes perhaps don't also indicate your approval.

Thank you for your feedback, I will not approve in the future any PR until all comments are reviewed (with other approvers/maintainers I assume that they will understand myself as I want this changes, but I trust them to do the changes and because they are simple enough I don't need a re-review).