Add additional checks to Health Monitor

[maxachis]

To ensure the Health Monitor is robust, we should add additional checks to ascertain health:

1. Key endpoints are responding (we already have this in the form of a search endpoint test)
2. Measure response times of search endpoint -- if latency is high, that's an issue
3. CPU, Memory Usage, Disk Space, and IO/Rates of Client VM and Database VM -- if these go over (and possibly under) certain limits, that's worth warning about.
4. Backend database is online and responding to simple queries

In addition, we want to be careful not to add too much clutter -- if the Backup Database is offline, then obviously CPU, Memory Usage, and other tests will fail as well, so we don't need all of those alerts firing off at once, and some should be suppressed if others are run.

In addition to adding these checks, we should then create tests to validate that these perform as expected.