Support boolean operators on tags in "tag" param on /api/v1/event/

[tristanjo-zillow]

Currently, tags for a given tagName are joined with an implicit "and," e.g.

/api/v1/event?tag=service:myservice&tag=specialTag:1&tag=specialTag:2

will only return events that are tagged with both ["specialTag:1", "specialTag:2"].

Enabling support for "or" and "not" would allow you to filter to events that matched one of several tags, or exclude events with a given tag.

Potential syntax could simply allow for urlencoded "&,|,!" as "and, or, not" respectively in the tag value along with parentheses delimiters, e.g.

service:service1&service2

service:service1|service2

service:!service1

service:(!service1|service2)&service3

Given that the app assumes a backing Mongo db, these can be parsed and mapped to Mongo queries against the "tag" array.

Potential lib for parsing the value: https://github.com/pyparsing/pyparsing