Menu a11y docs - add role and ariaselected attributes to tables

[thatblindgeye]

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Following https://github.com/patternfly/patternfly/issues/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.