Handle plugin updates

[jasonblalock]

Based on https://getinsomnia.slack.com/archives/CF69F4J7M/p1630085197002000, Insomnia does not have any mechanism for handling plugin updates beyond the user manually checking npm for new releases and then re-installing the plugin. It would be good if the plugin system was able to update automatically and/or let the user know that there's a plugin update available and ask if they'd like to update similar to other plugin systems (e.g. VSCode, etc).