Option to select an addon panel && rename selectedDownPanel to selectedAddonPanel

[usulpro]

Issue: #811

we had selectedDownPanel option in our UI module but it wasn't available by setOptions

What I did

Allow to set selectedDownPanel by setOptions.

Now it's possible to select the spesific addon panel this way:

setOptions({ selectedAddonPanel: 'storybook/notes/panel' })

You need to pass a panel ID to select a panel (same value that you pass to addons.addPanel())

If you don't know the ID you can pass anything and find in the console output the list of all registered
panels

How to test

run cra-kitchen-sink
Check out "Button" section. Selecting stories with different addons you'll see appropriate addon panels auto selected
Try to pass null or something else.

[codecov]

Codecov Report

Merging #1641 into master will increase coverage by 0.11%.
The diff coverage is 68.18%.

@@            Coverage Diff             @@
##           master    #1641      +/-   ##
==========================================
+ Coverage    21.3%   21.41%   +0.11%     
==========================================
  Files         244      244              
  Lines        5384     5402      +18     
  Branches      665      667       +2     
==========================================
+ Hits         1147     1157      +10     
- Misses       3732     3735       +3     
- Partials      505      510       +5

Impacted Files	Coverage Δ
lib/ui/src/modules/ui/configs/handle_routing.js	28.04% <100%> (ø)	⬆️
lib/ui/src/modules/ui/actions/ui.js	30% <100%> (ø)	⬆️
lib/ui/src/modules/ui/containers/down_panel.js	23.52% <100%> (ø)	⬆️
lib/ui/src/modules/api/actions/api.js	50.47% <63.15%> (+1.05%)	⬆️
lib/ui/src/libs/key_events.js	23.25% <0%> (ø)	⬆️
.../src/manager/containers/CommentsPanel/dataStore.js	34.78% <0%> (ø)	⬆️
addons/info/src/components/Props.js	37.2% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_keyevents.js	33.33% <0%> (ø)	⬆️
lib/ui/src/modules/ui/libs/filters.js	53.33% <0%> (ø)	⬆️
... and 14 more

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[Hypnosphi]

selectedAddonPanel maybe?

[usulpro]

Done!
I guess in glamorous components we'll rename all "down" to "addon" and "left" -> "stories"

[Hypnosphi]

LGTM

[matheo]

For the record (for those googling selectedAddonPanel)
it was moved to addons.setConfig({ selectedPanel }) on v5:
https://storybook.js.org/docs/configurations/options-parameter/