fix(code-server): add extensions to be auto-installed even when a cached copy of coder is found

[michaelbrewer]

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Currently when we find a cached copy of code-server we run it and exit early. But any requested extensions are not installed.

A solution would be to check if install_prefix/extensions or extensions_dir directories already exist before skipping ahead

[michaelbrewer]

@code-asher you where right. When bundling code-server then extensions won't be installed at start up.

I will make a fix for this