[feature] Add KFP Server Config to UI

[hmtosi]

/area frontend

UI Changes Following #680

UI should be adjusted so that

• The full KFP Server Config has a page in the settings menu where its fields can be adjusted. This includes
  • host
  • cookies
  • credentials
  • existing_token
  • namespace
  • ssl_ca_cert
• Connection is validated before use: When a user saves the new KFP endpoint, then Kale performs a connectivity check and surfaces a clear success or error message indicating whether the server is reachable and responding.
  • This is already occuring in the Kale panel, but it doesn't always reload when the config is saved - maybe make it so saving the config triggers the kfp connection check
• Invalid configuration is rejected gracefully: When the provided endpoint is malformed or unreachable, then Kale displays a descriptive error and does not attempt pipeline compilation or submission.
  • Grey out the Compile buttons if kfp server is not connected

UI test should be update to include this, and to ensure changes are loaded on the UI when a config is saved (we need to understand if a refresh is necessary)

[hmtosi]

/assign

[hmtosi]

Some things the UI development needs to take into consideration...

The current functionality of save_config allows save_config({"host": "http://new-host"}). This will overwrite the other config values to default. To update one config field at a time, the following needs to be called in order:
config = load_config() # Get existing values
config.host = "http://new-host" # Update just the host field
save_config(config) # Write all fields

Currently, the config is saved to .config/kale/kfp_server_json on the local machine where kale is running. The user is able to manually edit and save the config. This includes entering raw token or cookie data, which bypasses the validation. Thus, users could save sensitive data into the config and will not receive any kind of warning about it.