Update the plugin installation and management guide to v1.1.0

[FeynmanZhou]

Notation v1.1.0 offers Notation plugin management capabilities to simplify the plugin user experience.

• Added new command notation plugin install. Users are now able to install a notation plugin directly from a URL or from their file system. Supported plugin installation formats are .zip, .tar.gz, and single plugin executable file. See an example usage below:

$ notation plugin install --file <file_path>

$ notation plugin install --sha256sum <digest> --url <HTTPS_URL>

• Added new command notation plugin uninstall. Users are now able to uninstall a notation plugin by providing the plugin name. See an example usage below:

notation plugin uninstall <plugin_name>

The following plugins have been well tested with Notation plugin commands by Notary Project maintainers:

• AWS Signer plugin for Notation
• Azure Key Vault for Notation
• Venafi CodeSign Protect Signing Plugin for Notation

I tested these three plugin installation with notation v1.1.0. See this page as a reference: notaryproject/notation#869. We need to update the plugin guidance to reflect this feature.