Support change local environment to a agent based environment

[kailin4u]

Is your feature request related to a problem? Please describe

I want migrate only portainer Management to another machine ,with stacks remain to the origin machine.
I start the new portainer with backuped config successfully,however, the previous "local" environment should be a remote environment.
but i cant change the current 'local' env to a remote environment."Environment URL" is readonly.

if i add a new env, the exist stacks won't inherit, which is not what I want.

Describe the solution you'd like

allow to change a local env's Environment URL to a agent address.

Describe alternatives you've considered

allow to backup and import stacks config of a single env.

Additional context

No response