Add option to disable encryption when key is forgotten

[gschier]

Adds a way to disable encryption for a workspace when the user has forgotten their encryption key.

User Flow

1. User opens a workspace with encrypted values but no key configured
2. The "Enter Workspace Key" dialog appears
3. User clicks "Forgot your key?"
4. A confirmation dialog warns that encrypted values will fail to decrypt
5. User confirms, encryption is disabled, workspace becomes accessible
6. Any secure(...) values will show decrypt errors when used, allowing the user to fix them manually