adding search feature to users index page

Adding the search feature to the index page. User will now be able to go into the admin users page and do a query that will try to find any users that match. or partially match, on the name or email field.

/cc @zendesk/samson @pswadi-zendesk 

### References
 - Jira link: [Samson-94](https://zendesk.atlassian.net/browse/SAMSON-94)

### Risks
 - None
I will access this value on the UI side.
Is it a good practice to access those values directly from an erb template?
The main reason I actually created this method was because I thought that accessing the params in the view would not be a good practice.