feat: Use the theme flavor configured in the browser

[benjaminParisel]

• Use the theme flavor configured in the browser
• refactor header-theme.js file

Cover https://github.com/bonitasoft/bonita-documentation-theme/issues/128

[github-actions[bot]]

:recycle: PR Preview 7e5b501011bc2849c9ad76631d5b03f7c5c47c28 has been successfully destroyed since this PR has been closed.

_{🤖 By surge-preview}

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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