CLI: Improve add command & add tests

[ndelangen]

Closes #25871

What I did

I found that the add command contained a few quicks and bugs that I fixed.

• when adding a single digit version such as this: sb add package@1 it would install the latest version instead
• when adding a storybook package it wouldn't warn you when installing a specific version that isn't the current
• the logic to split a package+version specifier into a packageName & versionSpecifier wasn't setup to deal with scope packages

I added tests for the functionality of the add command.
The getVersionSpecifier function is tested separately, because regexes can be tricky, and it's faster to iterate on it this way if there is ever another bug with in.

I can remove the warning functionality if it isn't desired.
I figured i'd be nice to have because it would prevent it from later becoming an issue the user would have to fix with the doctor command.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

I've tested this manually in a sandbox via running the CLI directly from dist:

(next)⚡ [7] % node ../../code/lib/cli/bin/index.js add @chromatic-com/storybook@1.0.0
/Users/me/Projects/Storybook/mono/storybook/code/lib/cli/bin/index.js:23
  throw error;
  ^

Error: Addon @chromatic-com/storybook is already installed; we skipped adding it to your .storybook/main.ts.
    at add (/Users/me/Projects/Storybook/mono/storybook/code/lib/cli/dist/generate.js:3699:11)

Node.js v18.19.1
(next)⚡ [7] % node ../../code/lib/cli/bin/index.js add @storybook/addon-onboarding@1.0.0
/Users/me/Projects/Storybook/mono/storybook/code/lib/cli/bin/index.js:23
  throw error;
  ^

Error: Addon @storybook/addon-onboarding is already installed; we skipped adding it to your .storybook/main.ts.
    at add (/Users/me/Projects/Storybook/mono/storybook/code/lib/cli/dist/generate.js:3699:11)

Node.js v18.19.1
(next)⚡ [7] % node ../../code/lib/cli/bin/index.js add @storybook/addon-measure@1.0.0   
Verifying @storybook/addon-measure
Installing @storybook/addon-measure@^1.0.0
Adding '@storybook/addon-measure@1.0.0' to main.js addons field.
(next)⚡ % node ../../code/lib/cli/bin/index.js add @storybook/addon-measure      
Verifying @storybook/addon-measure
Installing @storybook/addon-measure@^8.0.0-rc.1
Adding '@storybook/addon-measure' to main.js addons field.
(next)⚡ %        

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

[ndelangen]

I extracted this, to be able to easily mock it in my test.

[valentinpalkovic]

Code-wise LGTM!