Added PreBuild Button configurable from Preference

[ashutoshpw]

Description

Added a Prebuild Button configurable from the Preference section of the plugin. Non-Github users can now initiate prebuild with one click.

Related Issue(s)

None

How to test

1. Install the Extension in your Browser
2. Go to Manage Extension Page and then on preferences
3. Check "Show PreBuild Option"
4. Visit any repository on gitlab.com
5. You will now see two extra buttons on the repository, one for opening the repository in Gitpod and another one for starting the pre-build of the repository.

[ashutoshpw]

@gtsiolis Does it need any more improvement for merging it to the main branch for the official release?

[orbulon]

Reviewed

[gtsiolis]

Hey @ashutoshpw! Sorry for coming back to this late, and thanks for giving this a go. 🙏

While we also experimented with extending the browser extension button with more options (see #59) we decided it's better to focus on improving onboarding through the dashboard with teams and projects which can provide better visibility of project prebuilds configuration, more user control, and more. In this context, we also intend to disable triggering prebuilds on arbitrary repositories, see gitpod-io/gitpod#4353.

I'll close this for now but do not let this discourage you from contributing to other areas of the product. You can also search for open issues related to the browser extension using the ~component: browser extension label.