feat: Add connection testing functionality for Rclone providers

- Introduced a new endpoint to test connections for source and destination providers.
- Implemented a TestResult component to display success or error messages based on connection outcomes.
- Enhanced the configuration form with buttons to initiate connection tests, improving user experience.
- Updated backend logic to handle connection testing and return appropriate feedback to the frontend.
- Refactored existing handlers and routes to accommodate the new testing functionality.

components/providers/common/common.templ

@@ -235,7 +235,7 @@ templ RcloneCommandOptionsContent(categoryMap map[string][]db.RcloneCommand, cat
 	<select id="command_id" name="command_id" x-model="commandId"
 		hx-get="/api/rclone/command-flags"
 		hx-target="#command-flags-container"
-		hx-trigger="load, change"
+		hx-trigger="change"
 		hx-include="[name='command_id']"
 		hx-vals={ fmt.Sprintf(`{"commandFlags": %s, "commandFlagValues": %s}`, commandFlagsJSON, commandFlagValuesJSON) }
 		@change="updateCommandRequirements()"