Configure integrations at the workspace level

[Artmann]

Integrations added through the extension UI are stored in SecretStorage keyed by Deepnote project, so the same database has to be configured again for every project in a workspace.

What already works

#440 added a file-based source: a .deepnote.env.yaml next to the .deepnote file or at the workspace root, with env: references resolved against .env and the process environment (setting deepnote.integrations.envFile.enabled, on by default). One file at the workspace root is effectively a workspace-level integration definition shared by every project under it, and it is applied to running kernels without a restart. It also matches what the CLI reads.

Remaining gap

There is no equivalent for integrations created through the UI:

• an integration configured in one project cannot be marked as workspace-wide;
• when adding an integration to another project there is no "use an existing integration" picker, so credentials are re-entered and stored twice.

Proposal

Either of:

1. A scope choice (project or workspace) when creating or editing an integration in the UI, with workspace-scoped entries applied to every project in the workspace.
2. An "Add existing integration" entry in the project's integrations list that links a SecretStorage integration already configured elsewhere in the workspace.

Until then the recommended route for shared integrations is the .deepnote.env.yaml file from #440.

[jamesbhobbs]

Narrowed the scope. #440 already gives a workspace-level way to define integrations through a .deepnote.env.yaml at the workspace root, which covers the original ask for anyone who can use a file. What remains is the UI and SecretStorage side: integrations created in the extension are still per project and cannot be shared or reused. The description now lists that gap and two possible shapes for the fix.