Backport of [ui] general keyboard navigation: 1.3.4 release into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #14138 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

The below text is copied from the body of the original PR.

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(Port of #12831 for pre-1.4 release)

A general Keyboard / Keynav service for the Nomad UI

• This allows Nomad users to navigate and operate their UI by use of keyboard alone and provides powerful defaults to move around:
  • absolute routes (such as g j to go to jobs index),
  • relative routes (such as shift + right-arrow to move to the next subnav section), and
  • dynamic routes (such as shift + 03 to go to the third link in a given list)
• Creates a new global modal, accessible by pressing ? anyplace in the app
• Gives users the choice to enable/disable shortcuts, or more advanced, to rebind individual commands to the pattern of their choosing.

Implementation and extension

• Establishes a keyboard service that emits a consumable buffer array and matchedCommand object
• Listens for keystrokes in any non-input elements
• On each keystroke, if the buffer matches a pattern/sequence in keyboard.keyCommands, that command's action is run. These actions can be any function, and are commonly router.transitionTo() objects.
• Uses Tether to place hints on-screen for when the user holds Shift
• Shortcuts can be added by use of modifier (such as the Go to ACLs link), or by use of component-level, conditional helper keyboard-commands (for example, how we conditionally add the escape key to Evaluations modal)
• Buffer clears after 0.75sec or when a successful keyboard command is executed

Side-effects

• In order to facilitate a u shortcut to "Go up a level" from nested routes, reworked many otherwise-inline subnavs into their own components, such as the plugin subnav
• In order to work around an Ember Router bug around LinkTos with query properties when deeply nested, invoked the classic linkTo component sparingly

Showing the keyboard modal (user pressed "?"):

Showing hints active (user holding "Shift"):

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