[EuiTooltip] Add an "alwaysVisible" prop

[sebelga]

In elastic/kibana#107292 @cchaos suggested to use a tooltip to give instruction on how to interact with the keyboard on a component. This works well except that, when the tooltip is shown if we mouse out it disappears.

I suggest that we add a new alwaysVisible optional prop to the <EuiToltip /> component which will always display the tooltip and not react to mouse events. The consumer would then be responsible to hide it if needed.

[cchaos]

For some clarification for whoever picks this up, the tooltip would be always visible only when the wrapped element is in :focus.

[hardikhere]

Can I pick this up? May be we can also add prop like disapearAfter={some value in milisec} what do you think
?

[cchaos]

So I've been thinking about solutions to this issue, remembering there was a "resolved" issue around closing tooltips on every mouse out/move, even when focused (#2560 & #3335). Looking at that specific issue, it seems the behavior being circumvented was when there were two or more elements in close proximity with tooltips and one is focused. I feel like most recently I've been more frustrated with tooltips closing when I don't want them to and seen less tooltips this close together.

@chandlerprall Since you were the one who originally opened the issue, was there more than just the overlapping tooltip issue?

My inclination, honestly, is just to revert #3335 or at least remove the mouse out/move listener when the element is focused.

[chandlerprall]

@cchaos it was only the fact that two tooltips were being displayed at the same time. I'm okay with reverting #3335