JetBrains: Add monochrome logo and use it in menus

Created by: vdavid

Fixes https://github.com/sourcegraph/sourcegraph/issues/37692

I think this is an optimal solution based on the discussion under the issue. I used the colors that JetBrains uses for their icons (both light and dark). It looks great on both dark and light themes. One caveat: for whatever reason, when I hover a menu item with our icon when a light theme is enabled, the IDE doesn't switch the logo to the brighter version. It's weird because I do the same that they do, the file naming is right, and the IDE can clearly find both the light and dark versions, so not sure why it doesn't use it when hovered. I think it's still much better than it was, though!

Test plan

• Loom

App preview:

• Web
• Storybook

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