[backend/frontend] login aside customization (#14115)

[esrevi]

Proposed changes

• Add new theme vars in Theme to handle customisation of the aside right panel on login
• Add new section in Theme creation, update drawer to be able to add a color, or a gradient color, or an image url or base64

Related issues

• Custom Right-Hand Side Background Image #14115

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case (coverage and e2e)
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

[codecov]

Codecov Report

❌ Patch coverage is 17.54386% with 94 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.35%. Comparing base (1fb52ee) to head (8c435aa).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...c/private/components/settings/themes/ThemeForm.tsx	0.00%	39 Missing ⚠️
...-front/src/public/components/login/LoginLayout.tsx	0.00%	15 Missing ⚠️
...vate/components/settings/themes/themeValidation.ts	0.00%	11 Missing ⚠️
.../opencti-graphql/src/modules/theme/theme-domain.ts	50.00%	8 Missing ⚠️
...rivate/components/settings/themes/ThemeEdition.tsx	0.00%	6 Missing ⚠️
.../private/components/settings/themes/theme-utils.ts	0.00%	6 Missing ⚠️
...ivate/components/settings/themes/ThemeCreation.tsx	0.00%	5 Missing ⚠️
...encti-graphql/src/modules/theme/theme-converter.ts	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14642      +/-   ##
==========================================
- Coverage   32.36%   32.35%   -0.02%     
==========================================
  Files        3096     3097       +1     
  Lines      210896   211072     +176     
  Branches    38196    38283      +87     
==========================================
+ Hits        68259    68283      +24     
- Misses     142637   142789     +152     

Flag	Coverage Δ
opencti-client-python	45.50% <ø> (ø)
opencti-front	2.82% <0.00%> (-0.01%)	⬇️
opencti-graphql	67.73% <62.50%> (+<0.01%)	⬆️

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[esrevi]

#14648