More efficient Registry module lookups

[radeksimko]

Background

#924 provides a way for us to do completion, hover etc. for any Registry-hosted modules without user having to install them, greatly improving the "out of the box" UX. This is achieved by gathering the module data from the Registry API for any parsed modules within any module which is open by the user.

For example

• pull all available versions from https://registry.terraform.io/v1/modules/puppetlabs/deployment/ec/versions
• pull metadata about the chosen version from https://registry.terraform.io/v1/modules/puppetlabs/deployment/ec/0.0.8

So this currently involves two API calls, both of which may potentially involve significant amount of data. We don't save more data than we need for the completion and hover, but all of it still needs to be downloaded from the API and decoded, resulting in potentially suboptimal memory/CPU/network-bandwidth consumption and poor UX for modules with many versions.

Proposal

• Build (v2) Registry module endpoint which allows version constraints matching on the server side, such that the client (language server but also TF Core) doesn't need to download all versions and loop over them.
• Use the new endpoint in LS