monitoring: fix alert state query, fix alert firing threshold

Created by: bobheadxi

Follows up https://github.com/sourcegraph/sourcegraph/pull/12395, https://github.com/sourcegraph/sourcegraph/pull/12483 both of which contained mistakes:

• the field for alert state is alertstate, not state
• alertQuery should only fire on >= 1 - see this query:

The above is critical_frontend_hard_error_search_responses, and:

• green line indicates actual value above critical threshold
• blue line indicates current, incorrectly triggered alerts (excluding times when it should actually be triggered)
• orange line indicates new query that correctly aligns with the value actually being above the critical threshold

Some more examples for sanity checks:

• warning_gitserver_running_git_commands
• warning_syntect-server_syntax_highlighting_timeouts