Handle the tags/admin/ client as an npm workspace at /tag-admin/

[eemeli]

This is a part of solving #2423.

As a first step, this PR separates the tag-admin front-end sources, build and dependencies into a new top-level directory /tag-admin/. The result of the build should not change at all, but the sources and configs are now more clear.

This introduces a dependency on npm v7 or later, as earlier versions did not support workspaces. Build & CI tasks are updated accordingly, in a few cases switching to use node-version: 16, as that includes a sufficient up-to-date npm. Some minor cleanup is done there also to favour npm ci over npm install, where appropriate.

The tag-admin contents or dependencies are left exactly as before, though a few files are renamed and the JS import statements are adjusted to use relative, fully qualified paths.

The following packages are removed from dev dependencies, as no actual usage for them could be identified:

"@babel/cli": "^7.13.10",
"@babel/plugin-proposal-class-properties": "^7.13.0",
"babel-plugin-transform-es2015-modules-commonjs": "^6.26.2",
"jsdom": "^11.12.0",
"react-test-renderer": "^16.14.0",
"request": "^2.88.2",
"style-loader": "^0.19.1",

NOTE: Because of the npm workspace config change, you may need to run rm -rf node_modules && npm install at the repo root in order to get the right topography after this is merged.

[mathjazz]

The new file & folder structure makes so much more sense and I'm already a fan of npm workspaces. :) Thanks!

I haven't been able to figure out why did the package-lock.json grow so big, though.

Is the plan to make frontend a workspace, too?

Might be a good idea to add a README.md file to the tag-admin folder, with a very short description of what it does and a linked explanation it's a npm workspace.

[mathjazz]

Nice :)

[eemeli]

I haven't been able to figure out why did the package-lock.json grow so big, though.

It's because the lockfile format is here updated to v2, which needs to duplicate all of the entries for backwards compatibility. v3 will eventually shrink it by half. The actual count of discrete items is reduced, though.

Is the plan to make frontend a workspace, too?

Yes, eventually. That would be a part of moving its package management from yarn to npm.

Might be a good idea to add a README.md file to the tag-admin folder, with a very short description of what it does and a linked explanation it's a npm workspace.

Is there an existing description of the tag admin tool available somewhere that could be used for this? If not, could you write a few words about it?

[Pike]

Would this be a good time to also yarn the tags UI instead of npm?

Using one and the other every now and then bothered me for a long time.

[eemeli]

Would this be a good time to also yarn the tags UI instead of npm?

Yes, but no? I'm actually working towards using npm also for the frontend.

[mathjazz]

Is there an existing description of the tag admin tool available somewhere that could be used for this? If not, could you write a few words about it?

# Tag Admin

This is an [npm workspace](https://docs.npmjs.com/cli/v7/using-npm/workspaces)
responsible for the tag management widget of the project administration page.

[mathjazz]

Could you please rebase?

[mathjazz]

\o/