[plugin] initialize ext storage proxy earlier

[akosyakov]

What it does

• fix Unknown actor StorageExt error #6305: Initialize ext storage proxy earlier. Otherwise the main side can send events before the plugin manager is initialized leading to exceptions.

How to test

• install some vs code extension, i.e. go
• open a project
• check that console dose not have unknown ext storage service errors

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

It worked successfully for me 👍

I tested using the bracket-pair-colorizer on master and with this change.
On master I could see the error Error: Unknown actor StorageExt, while with this PR, the error was no longer present.

[akosyakov]

Ideally we should not send preferences and storage information twice. Maybe we should just remove it from the plugin manager initialization, and initialize only in corresponding services. @benoitf ?

[benoitf]

AFAIK it was egg and chicken problem (cc @evidolob )