Menu a11y docs - add role and ariaselected attributes to tables

[thatblindgeye]

Following patternfly/patternfly#5799, we should update both HTML and React a11y docs to include verbiage about the role (on both the Menu and MenuItem), aria-selected, and aria-multiselectable. Since a consumer could use the Menu component to spec out their own custom Select, we should include these for them in a11y docs.