[gnodev] Notify user if there are conflicting deployments

[leohhhn]

Description

We need to notify the user in this case:

• The user deployed a package via msgaddpkg to path gno.land/r/xyz/pkg
• At some point, gnodev, through it's resolver, finds another package with the same package path
• It then deploys it with priority over the msgaddpkg one from the user.

This causes a peculiar situation in which people do not understand which package has been deployed and makes the case very confusing, which I've seen in practice about 3 or 4 times.

I suggest that we keep a list of manual AddPkg messages from the user, and in case the resolver finds a conflict, we notify the user that a conflict has happened and show the local/remote path from which the currently deployed package has been taken.

cc @gfanton