feat(console): help view modal

[hds]

Adds a help modal which is available on every view. The help help modal
can be accessed by pressing ? and overlays the current view. To leave
the help modal, the user can press ? or Esc.

This PR is based on #243 originally authored by @bIgBV. The previous PR
has been dormant for around a year.

Currently the help modal only displays a vertical list of controls. This
is the same information that is available in the controls widget on each
view.

Here is an example of the tasks view with the help view modal active:

connection: http://localhost:6669/ (CONNECTED)
views: t = tasks, r = resources
controls: select column (sort) = ←→ or h, l, scroll = ↑↓ or k, j,
view details = ↵, invert sort (highest/lowest) = i, scroll to top = gg,
scroll to bottom╭Help──────────────────────────────────────────╮t = q
╭Warnings───────│controls:                                     │───────────────╮
│⚠ 1 tasks have │  select column (sort) = ←→ or h, l           │               │
╰───────────────│  scroll = ↑↓ or k, j                         │───────────────╯
╭Tasks (12) ▶ Ru│  view details = ↵                            │───────────────╮
│Warn  ID  State│  invert sort (highest/lowest) = i            │t      Location│
│       19 ▶    │  scroll to top = gg                          │::task console-│
│       22 ⏸    │  scroll to bottom = G                        │::task console-│
│⚠ 1    23 ⏸    │  toggle pause = space                        │::task console-│
│       24 ⏸    │  toggle help = ?                             │::task console-│
│       25 ⏸    │  quit = q                                    │::task console-│
│       74 ⏹    │                                              │::task console-│
│       75 ⏸    │                                              │::task console-│
│       77 ⏸    │                                              │::task console-│
│       78 ⏸    ╰──────────────────────────────────────────────╯::task console-│
│       79 ⏹      wait      11s    4ms   56µs    11s 2     tokio::task console-│
╰──────────────────────────────────────────────────────────────────────────────╯

However, the idea is that the help modal can provide contextual
information depending on the view and the state of the application being
observed. This will allow us to provide more details about any lints
which are currently triggering and also to reduce the height of the
current controls widget to just one line (perhaps optionally) as the
full list of controls can be accessed from the help view.

Co-authored-by: bIgBV [email protected]

[hds]

This PR depends on #427, I'll rebase it once that has gone in.