Simplify the configuration service, enable programmatic modification

[egamma]

• simplify the configuration service
• enable programmatic modification (user, workspace)
• investigate if programmatic modification (tasks, debug) is needed

[bpasero]

Related:

• Should stop sending global settings and keybindings via IPC (Should stop sending global settings and keybindings via IPC #6094)
• IWorkspaceContextService should only exist on renderer side and have less functionality (IWorkspaceContextService should only exist on renderer side and have less functionality #6095)
• IConfigurationService should move back into shell (Move core services from main back into shell #6093)

[bpasero]

Done. Continue in #1396

[bpasero]

Reopening for supporting tasks and debug as well.