Version 5 refactor

[TooTallNate]

Changes include:

Major, breaking changes

• Callback signature has been removed. Only Promise based interface now.
• No more default export. Only named export getUri() is available now.
• Minimum Node.js version is now 14.x.
• The ftp:// protocol has been switched from ftp to basic-ftp module.
  • Closes switch ftp client? #16
  • Closes Dependency on 'ftp' causes [DEP0005] DeprecationWarning: Buffer() #18

Minor changes

• Proper options typings are now inferred based on the protocol of the URI provided to getUri(). For example: getUri('ftp://...') will have FtpOptions as the second parameter implicitly.
• A URL instance can now be provided as the first argument to getUri().

Misc

• Use pnpm for GH Actions.
• Use Jest for tests.
• Refactor tests to TypeScript.

[jimmywarting]

While making such a huge refactor, would it be good to switch to ESM then also?
it still compiles down to cjs...