Enable workspaces with linux/arm64
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MR: Pending
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## Description
Follow from the discussion here, https://gitlab.com/gitlab-org/gitlab-build-images/-/merge_requests/905#note_2566824178, we plan to provide full support for `linux/arm64`, which includes vscode fork build, workspace default image, and workspace tooling image.
We should exec in this sequence, 1) vscode fork build for arm64 2) workspace tools image for arm64 3) default image for arm64
Then we update GitLab repo altogether with ARM64 support. And also update workspace docs for related information.
For vscode fork build, the idea is to use one arm64 base image and build vscode fork on top of it. And pls see this issue for more details, https://gitlab.com/gitlab-org/gitlab-web-ide-vscode-fork/-/issues/53+
For tools image and default image, we should extend our current job in `gitlab-build-images`, and also resolve any potential issues raised with arm64 build.
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## Acceptance criteria
- [ ] Update tools image fetch asesst script to download for both `linux/arm64` and `linux/amd64`
- [ ] Update tools image CI to build for both platforms, and resolve any raising issues
- [ ] Update workspace default image to build for both platforms, and resolve any raising issues
- [ ] Update GitLab repo to remove image digest, and use image tag instead, so docker could decide to pull ARM64 or AMD64
- [ ] Test locally it works fine for ARM64, and also existing AMD64 works fine as well
- [ ] Update our doc to indicate both support, the requirement section, and more
## Implementation plan
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[Provide a high-level plan for implementation of this issue, including relevant technical and/or design details.]
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