[feat] more detailed search options

[cathteng]

Currently, the search bar on Flagr is limited to searching tags and descriptions. It would be nice if you could also search for specific constraints, i.e. searching for a specific constraint property name (property:property-name).

I ran into a case where I was modifying a method used to assign a value to a constraint property, and I had to manually check every single flag to see if that property was being used to make sure I wouldn't break anything. Adding this feature would save a lot of time in the future :)