Prepare for NPM publishing, update instructions for NPM and Soldeer

[ericglau]

• Updates package.json for publishing to NPM
  • Sets upgrades-core and defender-deploy-client-cli as peerDependencies, since those are often run but not always required (for example if users do not run upgrade safety checks or Defender)
  • Updates the package name to @openzeppelin/foundry-upgrades
    • Users can use the package name as @openzeppelin/foundry-upgrades in their Solidity scripts/tests, but we leave the examples as openzeppelin-foundry-upgrades and use remappings to avoid confusion (since the same instructions are also used for Git submodules or Soldeer)
• Adds instructions for NPM and Soldeer installations
  • While OpenZeppelin Contracts (and Upgradeable Contracts) could also be installed with NPM or Soldeer, we omit that from the instructions to avoid further confusion, since the steps are already complex

Fixes #40

[ernestognw]

If I understand correctly, the optionalDependencies is useful if we actively handle the lack of the dependency (see source). I would consider opening an issue, we can suggest installing them whenever required if they're dynamically imported.

[ernestognw]

Not sure how to bypass Snyk's check, perhaps an IT ticket is required. I would consider implement the dependency feedback handling but I wouldn't consider it a blocker.

Thanks

[ericglau]

Thanks. The intent was to mark those packages as compatible but not always required. They need to be installable when needed though. Changed it to peerDependencies as that more closely reflects this intent.