Add documentation for forcing OD UI

[samfreund]

Description

This describes how to force the OD UI for UI testing.

Meta

Merge checklist:

• Pull Request title is short, imperative summary of proposed changes
• The description documents the what and why
• If this PR changes behavior or adds a feature, user documentation is updated
• If this PR touches photon-serde, all messages have been regenerated and hashes have not changed unexpectedly
• If this PR touches configuration, this is backwards compatible with settings back to v2024.3.1
• If this PR touches pipeline settings or anything related to data exchange, the frontend typing is updated
• If this PR addresses a bug, a regression test for it is added

[Gold856]

Personally, I like editing GeneralSettingsView.vue and removing v-if="useSettingsStore().general.supportedBackends.length > 0" to force the card to render. That way, you don't need the backend. Both methods can be included.