Reflect default values in (module & core) completion and hover

[radeksimko]

Background

We currently only use attribute type during completion and hover.

There are cases where completing or displaying default value would be helpful:

• module inputs
• attributes in the core schema, e.g. ssh for connection type

UX Implications

Completion

TODO - module inputs
TODO - connection block

Hover

TODO - module inputs
TODO - connection block

Proposal

• hcl-lang
  • schema: Introduce DefaultValue to AttributeSchema hcl-lang#120
• terraform-schema
  • Set DefaultValue for module inputs
  • Set DefaultValue where relevant within the core schema

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TODO: Create a separate issue to track defaults for provider (currently unavailable via gRPC and therefore JSON)