Allow specifying custom Blueprint command (with arguments)

I am developing inside Flatpak using awesome [extension by Bilal Elmoussaoui](https://open-vsx.org/extension/bilelmoussaoui/flatpak-vscode) and I'd like to run blueprint LSP from the Flatpak environment I am using. For now I had to make a hack to make a `~/.local/bin/blueprint-compiler` file with this
```sh
flatpak build .flatpak/repo/ $PWD/subprojects/blueprint-compiler/blueprint-compiler.py $@
```
so it will launch it from there.

Could you please provide an option where I can specify command to run the blueprint compiler?
Thanks.

Start by locating the extension's language-server launch configuration and how executable arguments are currently selected; the issue does not name a file or test. Add a configurable command that supports arguments, including the Flatpak build command shown in the report, and verify that the LSP launches through it.

Written by the indexing model from the issue text.