[frontend] fix file name in fintel template export form (#8336)

[Archidoit]

Last fixes for Fintel templates

• fix export file name at fintel template export generation (from Content tab of a container)
• changes in the Executive Summary built-in template

To test: be able to change the export file name when generating an html/pdf file from a fintel template

[labo-flg]

tested locally ok

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.30%. Comparing base (3ab4762) to head (73cfa68).
Report is 5 commits behind head on release/6.5.0.

Additional details and impacted files

@@              Coverage Diff               @@
##           release/6.5.0    #9807   +/-   ##
==============================================
  Coverage          64.29%   64.30%           
==============================================
  Files                655      655           
  Lines              62860    62883   +23     
  Branches            6954     6967   +13     
==============================================
+ Hits               40414    40434   +20     
- Misses             22446    22449    +3     

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