Notifications: Add 'regex' and 'notregex' capability to the Notification Rules

**Proposal:**
From https://github.com/influxdata/EAR/issues/1932
Add 'regex' and 'notregex' to the notification rule's list of operators.

**Current behavior:**
Describe what currently happens.
Create a notification rule via the UI; add a tag condition; observe that you can only select == as the operator.
Use the REST API to retrieve the notificationRule definition
Use the REST API to PUT an update to the notificationRule, changing the operator on the tagRule from equal to 'regex'
Observe a success response from your PUT request.
Go back to the InfluxDB UI and try to view your modified notification rule
Get an error message: "An InfluxDB error has occurred.
**
**Desired behavior:**
Create a notification rule via the UI; add a tag condition; be able to select the 'regex' operator';
Use the REST API to retrieve the notificationRule definition
Use the REST API to PUT an update to the notificationRule, changing the operator on the tagRule from equal to 'regex'
Observe a success response from your PUT request.
Go back to the InfluxDB UI and try to view your modified notification rule
View the modified notification rule sucessfully.