`plugin update`: Update all or a single plugin(s)

[mostafa]

The idea is to update a single plugin if mentioned or all of them. The intention here is to detect the plugin name and location and try to update everything, including the plugin binary, config parameters and its checksum. This can be achieved via two means:

1. The plugin name should include the GitHub profile along with the plugin name, like gatewayd-io/gatewayd-plugin-cache.
2. There should be a plugin registry (https://github.com/gatewayd-io/internal-proposals/issues/8) that records the metadata of the plugins along with their unique name, so that the update command can retrieve the latest information and decide whether to update the plugin or not.

For implementing either of the above, proper version management (#315) should be implemented by plugins and the GatewayD CLI.

Note There is a new feature in the plugin install command, introduced in #349, that will update an existing plugin with the same name if the user tries to install a plugin, either by passing the --update=true flag or by enabling interactive prompt (which is disabled by default). This feature ignores the version of the existing plugin.

[mostafa]

This is currently built into gatewayd plugin install command using the --update flag. Also, the recent changes to the command to install or update plugins using the URLs in the plugins' config file, gatewayd_plugins.yaml, makes this seemingly redundant. Yet, after moving into a proper registry like Harbor, this should be reimagined.