[supervisor] support multi-line environment variable in ssh

[iQQBot]

Description

Before we use ~/.ssh/supervisor_env to store user envvar in order to export to ssh terminal (it's required by vscode desktop and some user case)

But there have some problems with that, it's don't support multi-line environments (some thing like rsa private key...), if you set an environment variable with a multi-line value, you may cannot connection via ssh

This PR remove ~/.ssh/supervisor_env logic, instead we use SetEnv argument to support that.

Related Issue(s)

Fixes #13592

How to test

1. start a workspace in the preview environment
2. run gp env to set a multi-line env

gp env TEST='this 
is
a new line'

3. open a new workspace in the same context (the env will only affect in new workspace, and gp env only set it in same scope)
4. connect workspace via ssh, run env and export to see multi-line environment variable is work
5. open this workspace in vscode desktop, it should work same with before

Release Notes

Support multi-line environment variables in SSH

Documentation

Werft options:

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-integration-tests=all
  Valid options are all, workspace, webapp, ide

[werft-gitpod-dev-com]

started the job as gitpod-build-iqqbot-ssh-bug-in-supervisor-env-13592.5 because the annotations in the pull request description changed
(with .werft/ from main)

[mustard-mh]

Tested and works well in preview env Cannot connect via SSH

But in Dashboard, it's still one-line input. Will file an issue to track it

[mustard-mh]

Code LGTM, tested with Desktop/Browser/SSH all good

/hold

For confirmation of workspace

[mustard-mh]

It's merged = =, sorry, I should /hold without approval to avoid race ( Tide moves faster than before 🐶

[mustard-mh]

@aledbf Could you check the code again 🙏 ? And we can make a follow up PR to update if have some