provider is not found.
Previously a user would see the following error even if terraform was
only searching the local filesystem:
"provider registry registry.terraform.io does not have a provider named
...."
This PR adds a registry-specific error type and modifies the MultiSource
installer to check for registry errors. It will return the
registry-specific error message if there is one, but if not the error
message will list all locations searched.
Some sources make network requests that are likely to be slow, so this
wrapper type can cache previous responses for its lifetime in order to
speed up repeated requests for the same information.
Kristin Laemmert