[gp] Allow update of existing user-scoped env vars

[geropl]

Description

This PR does two things:

• drops references to the long-deleted API call getEnvVars
• introduces a new flag --scope=[user|repo] to allow update on already existing user-scoped environment variables

###Discussion:
Permissions on environment variables are delicated, as they touch on the "workspace as trust boundary" principle. So far we have been very careful do not allow any cross-repository/-workspace "cross-talk" on the API level.

I still feel the slight expansion to update existing, globally-visible env vars make sense.
Alternatively, we could introduce a property "globally writable" on env vars, to make this even more explicit. WDYT?

Related Issue(s)

Fixes ENT-529

How to test

• start a workspace here: https://gpl-529-scope-user.preview.gitpod-dev.com/workspaces
• run these commands:

gitpod /workspace/bel (master) $ gp env
gitpod /workspace/bel (master) $ gp env WS_ENV=test
WS_ENV=test
gitpod /workspace/bel (master) $ gp env --scope=user USER_ENV=test
jsonrpc2: code 403 message: operation not permitted: missing create permission on envVar

• the the user env var in the UI with value "something"

gitpod /workspace/bel (master) $ gp env --scope=user USER_ENV=test
USER_ENV=test
gitpod /workspace/bel (master) $ gp env
USER_ENV=test
WS_ENV=test

Documentation

Preview status

gitpod:summary

Build Options

Build

• /werft with-werft
  Run the build with werft instead of GHA
• leeway-no-cache
• /werft no-test
  Run Leeway with --dont-test

Publish

• /werft publish-to-npm
• /werft publish-to-jb-marketplace

Installer

• analytics=segment
• with-dedicated-emulation
• workspace-feature-flags
  Add desired feature flags to the end of the line above, space separated

Preview Environment / Integration Tests

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-large-vm
• /werft with-gce-vm
  If enabled this will create the environment on GCE infra
• /werft preemptible
  Saves cost. Untick this only if you're really sure you need a non-preemtible machine.
• with-integration-tests=all
  Valid options are all, workspace, webapp, ide, jetbrains, vscode, ssh. If enabled, with-preview and with-large-vm will be enabled.
• with-monitoring

/hold

[geropl]

@filiptronicek If you have some spare time, would ❤️ a review on this one!

[filiptronicek]

Code looks great and seems to work just fine in the preview environment. Left one minor comment, thanks!

[filiptronicek]

I think this would be nicer if we just passed down the scope instead of this boolean, we can reuse the envScope type.

[geropl]

/unhold