BREAKING CHANGE: add new update features

[mdonnalley]

• Adds --version flag
• Adds --interactive flag
• Adds --hard flag
• Adds hidden --available flag
• Removes --from-local (this is a breaking change)
• Fixes update logic. The original PR to remove the legacy update logic actually removed the new logic instead of the legacy.
• Removes unnecessary reexec method
• General cleanup and refactoring

Usage

update the oclif-example CLI

USAGE
  $ oclif-example update [CHANNEL] [--version <value> | --interactive] [--hard]

FLAGS
  --hard             Remove all existing versions before updating to new version.
  --interactive      Interactively select version to install. This is ignored if a channel is provided.
  --version=<value>  Install a specific version.

DESCRIPTION
  update the oclif-example CLI

EXAMPLES
  Update to the stable channel:

    $ oclif-example update stable

  Update to a specific version:

    $ oclif-example update --version 1.0.0

  Interactively select version:

    $ oclif-example update --interactive

  Remove all existing versions and install stable channel version:

    $ oclif-example update stable --hard

  Remove all existing versions and install specific version:

    $ oclif-example update --version 1.0.0 --hard

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