Plugin install screen enhancements

[sbrossie]

1. Operation Complete. Please Reload Page Message

• After installing a new plugin the "configured instances" section does not refresh (and no indication that we should refresh) -> NOK
• After starting a new plugin the "configured instances" section does not refresh but there is an indication that we should refresh 'Operation Complete. Please Reload Page' -> OK

2. The Upload Plugin screen with the custom URI needs some sane default values (what is a valid URI ?, what is a valid key ?). For the URI, it seems we only support scheme 'http', 'https', 'ws', or 'wss'. I could not install the payment-test-plugin. Should we also support a file scheme -- or we enforce to have a webserver?

[tungleduyxyz]

Hi @sbrossie @pierre ,
Should we redefine the requirements? This ticket is about 6 years old and is outdated with the new UI.
I see we had this PR linked to the issue: killbill/killbill-kpm-ui#11
cc: @reshmabidikar