[Monorepo] - Proclaim monorepo

[eapolinario]

Describe your changes

This PR proclaims the 7 modules introduced by #4012 as the new place for contribution.

The list of changes:

1. Rename the modules
2. Build single-binary and sandbox (both demo and old sandbox) using the local modules
3. Component CI checks moved from each repo
4. Changes to releases

Let's talk about each change separately.

Rename the modules

The rules that govern the publishing of multi-module repositories are described in Go Modules Reference - The Go Programming Language, more specifically:

If a module is defined in a subdirectory within the repository, that is, the module subdirectory portion of the module path is not empty, then each tag name must be prefixed with the module subdirectory, followed by a slash. For example, the module http://golang.org/x/tools/gopls is defined in the gopls subdirectory of the repository with root path http://golang.org/x/tools . The version v0.4.0 of that module must have the tag named gopls/v0.4.0 in that repository.

This essentially means that in a subsequent PR, the one where we deal with release, we'll need to generate a few more tags, one per-component.

This PR simply fixes the names of the modules and ensures that go replace directives point to each module. I manually tested the compilation of each component. A subsequent PR is going to fix the single-binary and the components Dockerfiles.

Build single-binary using local modules

Done in this stacked PR.

Component CI checks

Done as part of this stacked PR.

Changes to releases

edit: this is going to come in a separate PR. For now merges to master will not trigger image builds nor releases.

We're going to tag merges to master using semver versionsing, so these new tags will update the patch version and use that to create a new release. Exactly how we do currently in each component. These automatic releases are not going to create new helm releases.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

❗ No coverage uploaded for pull request base (master@6296beb). Click here to learn what that means.

❗ Current head 0acb9d8 differs from pull request most recent head 2f3bd55. Consider uploading reports for the commit 2f3bd55 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #4014   +/-   ##
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  Coverage          ?   59.19%           
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  Files             ?      549           
  Lines             ?    39512           
  Branches          ?        0           
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  Hits              ?    23388           
  Misses            ?    13822           
  Partials          ?     2302           

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[pingsutw]

LGTM, but there is a failing test