[DISCO-3228] Add metrics and logging for curated recommendations favicons

[Herraj]

References

JIRA: DISCO-3228

Description

Add metrics and logging for curated recommendations favicons hits and misses. This will allow us to better understand the success percentage and be able to add the missing icon urls manually for the urls that had a miss.

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[Herraj]

1- Should we do a separate log for each missed item or logging an array / list is fine?

2- Naming of the metric. This function already emits metrics but those are prefixed corpus_api.... Since this isn't related with the corpus api itself, thought I'd go with this.

[gruberb]

I think logging the list and the naming is fine. The only thing I am thinking of - Will we emit the same metrics over and over again? AFAIK, the cache is by date? So new feeds/items could be from the same URL, and therefore we would list the URLs again. But I guess this doesn't matter. And for the count: We would always count the same URLs, which I guess is also fine, because we want to know each day how many items we cannot serve.