feat(ui): Add the possibility to provide the application namespace at app creation

[OpenGuidou]

Feature part of #20820

Optional option to provide the application namespace, as it's already possible via the yaml view.

Checklist:

• [x] Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• [x] The title of the PR states what changed and the related issues number (used for the release note).
• [x] The title of the PR conforms to the Toolchain Guide
• [x] I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• [x] I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• [x] Does this PR require documentation updates?
• [x] I've updated documentation as required by this PR.
• [x] I have signed off all my commits as required by DCO
• [x] I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• [x] My build is green (troubleshooting builds).
• [x] My new feature complies with the feature status guidelines.
• [x] I have added a brief description of why this PR is necessary and/or what this PR solves.
• [x] Optional. My organization is added to USERS.md.
• [x] Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

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[speedfl]

Wondering why we did not do it earlier

LGTM