[ResponseOps][MW] Allow users to delete MWs

[cnasikas]

Maintenance windows can be archived from the UI but they cannot be deleted. We should allow users to delete MWs from the UI. There is already a Delete MW API.

DoD

• Use the existing DELETE /internal/alerting/rules/maintenance_window/{id} API to delete MWs from the UI.
• Add an action to the MW table so users will be able to delete MWs.
• Show a delete confirmation modal when users delete a MW from the UI.

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)