chore: Do not reinstall node_modules when updating vscode-workflow build

What does this MR do and why?

It prevents the gitlab-vscode-workflow extension build script from running npm install if a node_modules repository already exists.

Why When implementing changes in the language server project, we use npm link to test the development build either in the Desktop or Web Browser builds of the Workflow Extension. If the web-ide's Makefile runs npm install every time that the extension is re-built, the effects of the npm link command are lost. In other words, we need to avoid running npm install so we can preserve the symlink to the language server local repository.

How to reproduce this bug?

1. Follow the instructions to develop or debug the language server from the vscode-workflow-extension . Do this in the context of the Web IDE.
2. Run yarn start:example in The Web IDE.
3. Change a source file in the gitlab-lsp local repository.
4. Change a source file in the Web IDE project.
5. After this change (assuming you successfully symlinked the gitlab-lsp project), the Web IDE should contain the modifications made to the gitlab-lsp project.