feat: feature/Labels subgroups

[FrsECM]

PR fulfills these requirements

• [ x] Commit message(s) and PR title follows the format [fix|feat|ci|chore|doc]: TICKET-ID: Short description of change made ex. fix: DEV-XXXX: Removed inconsistent code usage causing intermittent errors
• Tests for the changes have been added/updated (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• Best efforts were made to ensure docs/code are concise and coherent (checked for spelling/grammatical errors, commented out code, debug logs etc.)
• Self-reviewed and ran all changes on a local instance (for bug fixes/features)

Change has impacts in these area(s)

(check all that apply)

• Product design
• Backend (Database)
• Backend (API)
• Frontend

Describe the reason for change

Often, we need more than one class when we annotate image. There can also be some group of labels that have a meaning.

For example, let's take the example of the plane image :

The plane can be white/red, Boeing/Airbus.
It can have only one color and only one manufacturer.

What does this fix?

With this fix, we are able to group labels in subgroups.
In this case, we will group labels in combo-boxes.

What is the new behavior?

The UI will automatically group labels in subgroup.
If we activate mode "multiple" :

• It will allow multiple labels in the main group (without subgroup)
• It will allow only one label per subgroup
  If we activate mode "subgroup":
• it will allow only one label in the main group
• It will allow only one label per subgroup

labelstudio_car_example.mp4

What is the current behavior?

It will unpack all options and it will be complicate to identify main and subgroups.

What libraries were added/updated?

None

Does this change affect performance?

No

Does this change affect security?

No

What alternative approaches were there?

It would have been possible to create a complex taxonomy but it's much more impactful.

What feature flags were used to cover this change?

???

Does this PR introduce a breaking change?

(check only one)

• Yes, and covered entirely by feature flag(s)
• Yes, and covered partially by feature flag(s)
• No
• [x ] Not sure (briefly explain the situation below)

For me it's not a major change because the old behavior is not impacted.

What level of testing was included in the change?

(check all that apply)

• e2e
• integration
• unit

Which logical domain(s) does this change affect?

It will allow to annotate more precisely when we have "nested" classes on an object.

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