cmd: add remotesource delete command

[camandel]

Add a subcommand to delete a remotesource:

agola remotesource delete --name <remotesource-name>

[sgotti]

@camandel Thanks for the PR!

The command wasn't implemented by purpose (while as you can see there's already an api to do this) because deleting a remote source will invalidate all the user linked accounts and consequently all the projects connected with that linked account.

Deleting a remote source isn't usually an operation the should be done (usually an user wants to update the remote source, and this is already possible).

For the user the effects of deleting a remote source are that it won't be able to login anymore via oauth with the remote source: The solution to let the user continue logging in with local auth (#23) or external auth (#24).

For a project the effects of deleting a remote source are that its linked account will be invalidated and agola won't be able to update commit statuses or reconfigure the project deploy key and webhooks (if requested) making the project unusable (please note that it's already possible to update a project linked account but it requires the same remote source. One could think to add the ability
to change a project linked account using a different remote source but this doesn't makes a great sense since the projects is very tied to the remote source repository (remote repository id and path)).

In the end, my opinion is to currently add a big warning when doing a remote source deletion and adding a confirmation dialog (overridable with a -y flag) and document the effects on doing this operation in the doc at https://agola.io

[camandel]

@sgotti Thanks for the detailed explanation.
In reason of all potential problems that "remotesource delete" could create (compared to benefits), I think it safer to not include this PR.

[sgotti]

@camandel I'm quite sure other users will ask for this. So the first step will be to better document the effects of removing a remotesource and think/implement possible solutions to improve users/projects management in case there's the need to delete a remotesource. I'll open a related issue. Then we could add the delete command.