feat: improve logging for plugin selection and scoring

[Xunzhuo]

Fixes: #1170

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[nirrozenbaum]

@Xunzhuo thanks for this PR.
I was thinking about using String() function to return a descriptive string (maybe in json format or something like that), and then being able to log it using just name-value pairs.

current approach lacks the contextual logging (we don't use log.FromContext(ctx)), which might be helpful in some cases.

wdyt?