feat(system): gpicase2: support docked mode on retroflag gpicase2 (at boot only)

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• if the Merge Request is about a new feature, an improvement or an important bugfix, amend RELEASE-NOTES.md
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Changes :

• Add script for support of Retroflag GPI Case 2 (at boot only)
  • unset in-case pad when HDMI is connected
  • audio switching between in-case and HDMI
  • Switch to recalbox-next theme when docked

Related to :

• #2358
• #2364