model/labels: fix regex with capture, wildcards, literal (#17828)

This change fixes an issue introduced in #17707. When a regex
with a wildcard, literal, and final wildcard surounded by a
capture group was parsed - the capture group was not removed
first preventing `optimizeConcatRegex` from running.

Found via fuzz testing.

Signed-off-by: Nick Pillitteri <nick.pillitteri@grafana.com>

model/labels/regexp.go

@@ -71,6 +71,10 @@ func NewFastRegexMatcher(v string) (*FastRegexMatcher, error) {
 		if err != nil {
 			return nil, err
 		}
+
+		// Remove any capture operations before trying to optimize the remaining operations.
+		clearCapture(parsed)
+
 		if parsed.Op == syntax.OpConcat {
 			m.prefix, m.suffix, m.contains = optimizeConcatRegex(parsed)
 		}

model/labels/regexp_test.go

@@ -93,6 +93,7 @@ var (
 		"(.+)-(.+)-(.+)-(.+)-(.+)",
 		"((.*))(?i:f)((.*))o((.*))o((.*))",
 		"((.*))f((.*))(?i:o)((.*))o((.*))",
+		"(.*0.*)",
 	}
 	values = []string{
 		"foo", " foo bar", "bar", "buzz\nbar", "bar foo", "bfoo", "\n", "\nfoo", "foo\n", "hello foo world", "hello foo\n world", "",