Add RegularExpressionTestUtil for testing regexes

[ldhardy]

There are multiple places we're doing something similar to test regex, and plenty of places we need to, but are not yet. It would be nice to clean it all up and use one utility class. Needed for another effort.

[drivenflywheel]

Looks like a good addition. We should add at least cursory test coverage now to ensure that future regressions that are accidentally introduced will get caught prior to downstream integration.

[drivenflywheel]

This diff looks to have gone a bit wonky. Lots of out-of-scope files now showing up as changed

[ldhardy]

should be good now. Just one file.

[dev-mlb]

#14 67.84 /opt/emissary/src/test/java/emissary/test/util/RegularExpressionTestUtil.java:[19,7] [PrivateConstructorForUtilityClass] Classes which are not intended to be instantiated should be made non-instantiable with a private constructor. This includes utility classes (classes with only static members), and the main class.
#14 67.84     (see https://errorprone.info/bugpattern/PrivateConstructorForUtilityClass)
#14 67.84   Did you mean 'public final class RegularExpressionTestUtil {'?
#14 67.84 [WARNING] /opt/emissary/src/test/java/emissary/test/util/RegularExpressionTestUtil.java:[20,28] [NonFinalStaticField] Static fields should almost always be final.
#14 67.84     (see https://errorprone.info/bugpattern/NonFinalStaticField)

Dismiss stale review.