fix: annotation scraping - scrape_port_named_metrics and metrics.grafana.com/port

[adamhackl]

2 fixes in modules/kubernetes/annotations/metrics.alloy

• In one of the first steps, __tmp_scrape is default set to false, but the next step watches for metrics.grafana.com/scrape to be blank or true and then makes the value of __tmp_scrape = true. So __tmp_scrape would never be blank. But the step that runs if the attribute scrape_port_named_metrics = true only runs if __tmp_scrape is true or blank. The point of that attribute is to scrape any port that contains the word metrics in its name, regardless of the metrics.grafana.com/scrape attribute, but it was not working that way since it could never be blank. We only want that step to not run if metrics.grafana.com/scrape = false, which it is now only set to __tmp_scrape if the attribute is set to false, not just by default.
• The step that watches for metrics.grafana.com/port to be set to override the __address__ port had an additional source label added to it when it was copied from grafana-agent-modules, but the regex was not adjusted to account for the additional label, so the step would never work.