Respect XDG Base Directory Specification

On Linux, the Red Hat telemetry functionality creates the .redhat directory in the home directory. Most importantly, this directory contains anonymousId; see USAGE_DATA.md and https://github.com/redhat-developer/vscode-redhat-telemetry/blob/d5737dc1096f8220c2e10287e774f4dec3be45b5/src/node/fileSystemIdManager.ts#L46

This unfortunately adds to the problem of the home directory filling up with hidden dotfiles. As a better way of organizing the home directory, the XDG Base Directory Specification is widely used.

For those of us who value a clean home directory, I hope you can consider a few options:

• Creating the redhat directory relative to an appropriate XDG Base Directory, if specified in the user environment;
• Providing users with the option to explicitly specify the location of the redhat directory using a dedicated environment variable

Changing this would affect more projects, including but not limited to:

• Quarkus adds some additional files to the .redhat directory. See https://quarkus.io/guides/build-analytics.
• Needs changes in the Java telemetry project too; see https://github.com/redhat-developer/intellij-redhat-telemetry/issues/84.

Start with src/node/fileSystemIdManager.ts at the referenced location and review USAGE_DATA.md alongside the XDG Base Directory Specification. Define which XDG location or dedicated environment variable should control the redhat directory, then confirm the Linux telemetry behavior and related documentation reflect the decided approach.