[Metrics UI] Metrics threshold stores malformed KQL as an empty filter

[jasonrhodes]

Summary

In the Metrics Threshold rule type, a user can add a KQL string filter to narrow down the results of a query for the rule to evaluate. It looks like this:

If you take this same exact filter seen here and apply it in the Discover KQL bar and push "Enter", you'll see the following error:

Expected AND, OR, end of input, whitespace but "A" found. host.name: (hyperion.local)AND host.architecture: "x86_64" ---------------------------^

Unfortunately, the KQL bar in the rule type create/edit dialogue doesn't catch this particular validation error. More importantly, when we attempt to parse the filter, we swallow any errors we encounter. This means that a malformed KQL string can be saved in the saved object's filterQuery field as '', even when that saved object's filterQueryText field (the raw string entered and shown in the create/edit UI) is not empty.

Since this filter is very important for a rule to work as intended, we need to be sure we validate this on the client side and stop swallowing errors we encounter while parsing the value.

Acceptance Criteria

• KQL is validated on the client to the same degree as is being done in Discover, currently
• Errors encountered while attempting to parse the filterQueryString should not be swallowed

Note: we should check our other rule types to see if this problem exists elsewhere, as well.

[elasticmachine]

Pinging @elastic/infra-monitoring-ui (Team:Infra Monitoring UI)