feat(init): default useNx and useWorkspaces to true for new lerna workspaces

[fahslaj]

When initializing lerna for the first time with lerna init, workspaces and nx will both be enabled by default.

Description

For lerna init:

• default useNx to true
• default useWorkspaces to true
• automatically add nx as a dev dependency if useNx will be true
• automatically add workspaces property to package.json if useWorkspaces will be true
• explicitly set useNx to false if lerna.json already exists and useNx is not set
• explicitly set useWorkspaces to false if lerna.json already exists and useWorkspaces is not set
• fix a bug where useNx was being reset to false whenever lerna init was run on an existing workspace with useNx: true
• refactor ensurePackageJson() and ensureLernaConfig() into one ensureConfig() function to reduce surface area for bugs in configuration that spans both config files (such as workspaces)
• add an informational message upon successful initialization that links the user to the lerna docs

For all commands:

• add a warning to the console when a command is run and lerna does not have either:
  • useWorkspaces: true in lerna.json AND a workspaces property set in package.json
  • packages property set in lerna.json
• add a warning to the console when workspaces are defined in package.json, but lerna.json does not have useWorkspaces: true

For the docs:

• updated the getting started guide to no longer describe needing to install nx manually on a newly created lerna project

For lerna --help

• update the link to point to the new docs

Motivation and Context

This change enables two of lerna's most powerful features by default - the ability to run commands with nx and the ability to make use of Yarn/npm workspaces by default for detecting packages.

How Has This Been Tested?

Extensive unit, integration, and e2e tests have been added. I have also manually tested the lerna init command for each of these scenarios.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (change that has absolutely no effect on users)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[JamesHenry]

Per slack discussion

[AviVahl]

This installs nx and its many dependencies (some of which are requesting exact versions) to any project using lerna, even if they don't use nx. 👎

Even stuff that I wouldn't expect like tsconfig-paths and @parcel/watcher are now being installed.