[BUG] No way of specifying `base_environment` for serverless compute (e.g. for ML serverless)

[ATherkel]

Describe the bug
When selecting serverless compute, it is not possible to specify the base_environment. This has the side effect that it is currently not possible to run ML serverless from VSCode. As such, e.g. integration tests using ML functionality cannot be executed from VSCode on a serverless compute.

I have not been able to do it with databricks-connect either.

To Reproduce
Steps to reproduce the behavior:

1. Go to the Databricks extension
2. Click on "Select Cluster"
3. Select Serverless
4. ... there are now nowhere to specify the base_environment. Here, I would like to be able to specify e.g. base_environment = "databricks_ml_v5"

Screenshots

From Databricks:

System information:

1. Paste the output of the Help: About command (CMD-Shift-P).

   Version: 1.123.2 (user setup)
   Commit: 3c631b164c239e7aeaaae7c626b46c527b361af2
   Date: 2026-06-09T15:06:40-07:00
   Electron: 42.2.0
   ElectronBuildId: 14159160
   Chromium: 148.0.7778.97
   Node.js: 24.15.0
   V8: 14.8.178.14-electron.0
   OS: Windows_NT x64 10.0.26200
   

2. Databricks Extension Version
   2.11.0
   Databricks Extension Logs
   N/A

Additional context
Add any other context about the problem here.

[ATherkel]

feature-request would probably have been more appropriate than the bug label. Sorry about that.