feat: Interactive 'uc ctx connection` command to select preferred cluster connection (#170)

* feat: Interactive uc command to select preferred cluster connection

https://github.com/psviderski/uncloud/issues/125

* Simplify connection selection and reordering by using the index instead of a pointer

* Move connection reordering logic to a new SetDefaultConnection on context

internal/cli/config/context.go

@@ -4,3 +4,21 @@ type Context struct {
 	Name        string              `yaml:"-"`
 	Connections []MachineConnection `yaml:"connections"`
 }
+
+func (c *Context) SetDefaultConnection(index int) {
+	// Do nothing if the index is out of range.
+	if index < 0 || index >= len(c.Connections) {
+		return
+	}
+
+	selected := c.Connections[index]
+	newConnections := make([]MachineConnection, 0, len(c.Connections))
+	newConnections = append(newConnections, selected)
+
+	for i, conn := range c.Connections {
+		if i != index {
+			newConnections = append(newConnections, conn)
+		}
+	}
+	c.Connections = newConnections
+}