Add Skaffold trigger options: uffizzi dev start --trigger polling add --trigger manual

[gadkins]

Summary

• Add the --trigger option to uffizzi dev start command to have parity with the Skaffold dev command.
• Document why the trigger option exists (see Context below)

Context

Skaffold's default trigger for syncing the files - I was testing running the uffizzi dev start initially on Ubuntu WSL, and you might remember I had mentioned that the changes were not syncing when the environment was started with uffizzi dev start and so I was testing with skaffold dev. The “sync” functionaly within Skaffold uses the “notify” trigger as a default way for syncing changes, which does not work for Window Subsystems. I tested it out on a Linux OS and the changes were syncing as they should. I was running skaffold dev (on WSL) with another argument to the command. It is the --trigger argument. Skaffold supports 3 different options for triggering the syncing of files - notify (the default), polling and manual. So a functioning sync using Skaffold would look like skaffold dev --trigger polling (on WSL). Our build_skaffold_dev command goes with the default trigger option, which is the notify method, which does not work for WSL (did not check on Mac). Might be a good idea to give users the flexibility to pass this option with the uffizzi dev start command, and also perhaps edit the documentation as to why an additional flag (--trigger) might be needed for other environments.