Monitor charts: Validate form for creating an alert before submitting

What does this MR do?

Fixes issues with alert modals described in #31904 (closed)

• Prevents triggering a premature modal dismissal on errors
• Prevents errors from disabling fields in alert modal
• Selects a default operator to help the user make the right choice
• Places the error message with correct spacing

Please review with environment_metrics_additional_panel_types FF on

Screenshots

before	after
Error dismissed modal, locked the modal fields	Error handling in modal
User must select operator on new alert	Default operator set on new
	Error message in modal and panel (left in panel if the error occurs on load

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [ ] Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Related to #31904 (closed)