a11y: Fix keyboard navigation, aria label/role and focus display for app bar

[nwmac]

a11y Issue: 18, 1, 19

1. The app bar button (see below) does not show keyboard and focus presentation.
2. The pin/unpin icon is missing aria-label and role attributes.

See below for screen shot.

All of the items in the app bar should show focus appropriately and should support keyboard navigation (enter/space to activate).

Additionally, when expanded, the pin/unpin icon should support keyboard navigation and focus appropriately.

Pin/Unpin:

Issue 19: A focus indicator is not visually available as user tabs through mentioned instances using a keyboard resulting in users with learning and mobility impairments as well as those with low vision not being able to easily find out which element currently has the focus.

[yonasberhe23]

Needs manual validation at this time as we dont have existing accessiblity tests. Follow-up ticket to create automated tests coverage rancher/qa-tasks#1639

[IsaSih]

Navigation using tab and return work as expected in
Rancher | v2.11-1e40bc40c55a020fc67dc3c3dde47b41dc94caf1-head
Dashboard | master 574248d
Rancher CLI | v2.11.0-rc.1
Helm | dev
Machine | v0.15.0-rancher125

However, the space bar clicks the burguer menu and the pin icon, but does not perform click actions in elements inside the app menu.

[aalves08]

The decision made is that "links" that appear as buttons are to have the space key as trigger as simple links, anchors, non-button links should not have the space key as trigger, as per #12959 (comment) + #12959 (comment)

[aalves08]

@IsaSih given the reply from a few weeks ago do you agree we can close this? FYI @rak-phillip @nwmac