feat: Fix MultiLayer Image display

[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.)
• [x ] 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)
• [ x] Frontend

Describe the reason for change

When using multilayered images. Often the gallery is not visible when dealing with large images.

What does this fix?

The fix moves toggle button near the toolbar in order it to be everytime visible.

New behavior :

labelstudio_pdd_example.mp4

What is the new behavior?

The new behavior is very similar to the old one. Just the buttons are in another place and sticky.

What is the current behavior?

In the current behavior, buttons can be hidden and we need to scroll up/down to access it.
By doing so, most of the time we lose buttons in order to select labels what is anoying.

What libraries were added/updated?

None

Does this change affect performance?

It improve labellers performance.

Does this change affect security?

No

What alternative approaches were there?

Display everytime buttons, but if doing so, we'll lose some place for the image.

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 breaking changes.

What level of testing was included in the change?

(check all that apply)

• e2e
• integration
• unit

Which logical domain(s) does this change affect?

Annotation of multilayer images.

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