Database: Add connection auto-completion

[seclerp]

Currently, the Connection input field is just a regular editable text control. It doesn't provide the ability to select available connections rather than entering them manually.

We need to replace it with an editable combo box with known values.

Implementation status

Per-project configuration sources

• appsettings*.json files located in a startup project folder
• User secrets file of a startup project

Data sources from Database plugin (Reported in #146)

• SQLite
• Postgres
• MS SQL
• MySQL
• Oracle

Other

• "Got it" notification for users to notice the feature (near Connection field)

Visual representation