Allow to add/edit multiple blades from signage form with a formset

[PartyNell]

Description

Add a form set in the 'Signage' form to add and edit all the blades of a sign at the same time. As before, lines can be added or edited from the blade form.

Related Issue

Ajout d'un formset des lames dans le formulaire signalétique #5511

Checklist

• I have followed the guidelines in our Contributing document
• My code respects the Definition of done available in the Development section of the documentation
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes
• I added an entry in the changelog file
• My commits are all using prefix convention (emoji + tag name) and references associated issues
• I added a label to the PR corresponding to the perimeter of my contribution
• The title of my PR mentionned the issue associated

AI requirements

Skip the checkboxes below 👇 If you didn't use AI for your contribution

• I used AI assistance to produce part or all of this contribution
• I have read, reviewed, understood and can explain the code I am submitting
• I can explain and discuss my work to a maintainer
• I pasted the prompt used and mentioned the model used below

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.54%. Comparing base (85802a3) to head (b7e602d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5641   +/-   ##
=======================================
  Coverage   98.53%   98.54%           
=======================================
  Files         274      274           
  Lines       23006    23025   +19     
=======================================
+ Hits        22670    22690   +20     
+ Misses        336      335    -1     

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[cypress]

Geotrek-admin    Run #17628

Run Properties:   Passed #17628  •  131c5742ac ℹ️: Merge b7e602de169045b11703b8abf57e8325dbff6da4 into 85802a387276ec95d97c36707404...

Project	Geotrek-admin
Branch Review	refs/pull/5641/merge
Run status	Passed #17628
Run duration	02m 14s
Commit	131c5742ac ℹ️: Merge b7e602de169045b11703b8abf57e8325dbff6da4 into 85802a387276ec95d97c36707404...
Committer	Nell Party
View all properties for this run ↗︎

---

Test results
Failures	0
Flaky	0
Pending	0
Skipped	0
Passing	22
View all changes introduced in this branch ↗︎