AWS Toolkit management settings should perform client side validation and be adaptive based on what is allowed/disallowed

Attached is a screenshot and in this context, I am allowed to change the number of instances and actually hit the Apply button with a **Single Instance** environment. Yes, it goes through an environment update process, as shown by logs below, but at the end my instance count is still at 1 because its a Single Instance environment. This is very deceiving and easily throws me off as a user.

Time | Type | Details
-- | -- | --
2020-04-09 10:33:51 UTC-0700 | INFO | Environment update completed successfully.
2020-04-09 10:33:51 UTC-0700 | INFO | Successfully deployed new configuration to environment.
2020-04-09 10:32:44 UTC-0700 | INFO | Updating environment EBLabA-prod's configuration settings.
2020-04-09 10:32:37 UTC-0700 | INFO | Environment update is starting.

Compare this with the web console which is much more intuitive


No source files, tests, or entry points are named. Reproduce the management-settings flow with a Single Instance environment and compare it with the web-console screenshots; done means disallowed settings are identified before Apply and the controls or validation prevent misleading environment updates.

Written by the indexing model from the issue text.