Improve efficiency of keyword search on events

A single keyword filter is currently implemented as an OR condition group with CONTAINS queries across multiple fields. To simplify this query and make it more forgivable, we should save a sanitized keyword field to event entities and query that directly.

Technical Approach

Server Side

1. Create a new base field on events called (keywords?) See hook_entity_bundle_fields_info_alter
2. Implement hook_node_presave on events to update that field with a concatenated version of
   1. Title
   2. Content
   3. Intro
   4. Teaser
   5. Event tag titles
3. Sanitize that field to remove special characters and trim white space
4. Implement hook_taxonomy_term_update to update all events when their corresponding event tags have been edited
5. Implement a queue worker to prevent overloading the server with a lot of event update operations See polaris_search module

Client Side

1. Update keyword filter method to query the single field
2. Ensure the keyword is sanitized before making the request