feat: update code-server and extensions in jupyterlab

[vexingly]

Add the databricks and some other useful extensions by default, bump up the code-server version to latest as required by the databricks extension. The latest databricks extension is needed to configure storage accounts as an output location!

[vexingly]

Changes in current PR:

• Add cache step to workflow to try to speed up builds (untested)
• Add mamba library to speed up conda env setup
• • Use mamba for conda env setup
• Fix global pip timeout not getting persisted to reduce error messages from artifactory
• Fix AMD AOCL libraries not getting setup
• Update VS Code to latest version in jupyterlab image (remote-desktop is currently being rebuilt)
• Update default extensions that we install (new versions and new extensions)
• Fix process to install extensions and default user settings (move directory back under /home/jovyan/)
• Add R language server install to get rid of VS Code nag message on startup
• Update default theme to new VS Code default (otherwise it nags you on first startup)