Add regex matching to resource attribute filters

[damemi]

Fixes #447 by adding a Regex field to resource filters. There are no restrictions on this field, so for example it is ok to set Prefix and Regex. The code will simply do an OR check if one of them matches.

[dashpole]

I would personally expect AND behavior if I put two conditions together, and OR behavior if I put two conditions separately.

[dashpole]

But then again, a regex is strictly more expressive than a prefix, so its probably fine to take either approach. Or we could only allow one of [Prefix, regex] and leave our options open for the future

[dashpole]

I'll leave the decision up to you.

[damemi]

I like it. To your point about expressiveness, I can't think of a case where someone would want to AND a prefix+regex that couldn't be expressed in one regex. But I could see the separation making configs a little more readable, if someone chooses to do that.

Made the change, please double check my logic makes sense.

[dashpole]

Suggested change

	matchesRegex = matched
	}
	if strings.HasPrefix(k, resourceFilter.Prefix) && matchesRegex {
	if !matched {
	continue
	}
	}
	if strings.HasPrefix(k, resourceFilter.Prefix) {

Seems simpler not to track matchesRegex separately

[damemi]

Taking out the error handling made it easier for me to just do both checks in the if. I had trouble reusing the matched variable from the regexp call because I was declaring a new err on the same line. It's better now