mt-action-menu: initial open orientation and gap to trigger

[fabianhueske]

Package: @meteor/component-library

Improve mt-action-menu with control over its initial open direction and the spacing to the trigger.

Proposed improvement

• Add an initial open orientation (e.g. top/bottom/left/right, or start/end) to control where the menu opens relative to the trigger
• Keep collision handling/auto-flip as fallback when the preferred orientation doesn't fit
• Add a configurable gap/offset between the trigger and the menu (token-based default)
• Document the new props with examples in Storybook