Add EnableApplication rpc for grpc api service

[kurochan]

What this PR does / why we need it:
Support enable application operation through grpc api.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

Add EnableApplication rpc for grpc api service

[khanhtc1202]

Hi @kurochan thanks for your contribution 😁
Could you share the purpose of this PR? Since this PR only add rpc to grpc api (backend to handle pipectl request) we need to add pipectl imp as the caller side if you want to use this rpc 👀

fyi, this is the pipectl caller side impl for disable apps command
https://github.com/pipe-cd/pipecd/blob/master/pkg/app/pipectl/cmd/application/disable.go

[kurochan]

@khanhtc1202 I'm trying to developing terraform provider for pipecd. In the process of that, I found there are no function to enable applications.

Should I implement pipectl command in this PR?

[khanhtc1202]

I'm trying to developing terraform provider for pipecd. In the process of that, I found there are no function to enable applications.

I see, if you plan to connect to this rpc directly (not via pipectl) then it's fine to not implement pipectl command.

[khanhtc1202]

lgtm 👌