Remote extensions updates for 1.41

[Chuxel]

There are quite a few updates for 1.41 given some new features and properties that were added to devcontainer.json. This PR makes the following updates:

Containers:

• ARM32 and ARM64 support. Using remote containers on ARMv64 (Jetson Nano) fails (wrongly installs vscode-server-linux-64) vscode-remote-release#1716
• SSH agent forwarding. devcontainer.json option to forward SSH agent or provide SSH keys inside the container vscode-remote-release#106 (comment)
• Extensions folder can be mounted direct. Add option to use volume to avoid reinstalling extensions, VS Code Server on container rebuild vscode-remote-release#421 (comment)
• Updated use of remoteEnv, containerEnv for env vars (affects lots of places) over runArgs
• Recommend remoteUser, containerUser over runArgs. Document UID/GID update behaviors. Also recommend the use of remoteUser over modifying Docker Compose files in most cases.
• Recommend using mounts over runArgs (affects several places)
• Add a subset of these properties along with settings to the attached config sections
• Reference ssh:// support in section on remote docker hosts

(Related issue: microsoft/vscode-remote-release#1923)