community: add go backend example

[arjunyel]

Description

Add a Go backend sample app

Changelog

• [ ] CHANGELOG.md is updated with user-facing content relevant to this PR. If no changelog is required, then add the no-changelog-required label.

Affected components

• [X] Community Content

Server checklist

Catalog upgrade

Does this PR change Hasura Catalog version?

• [X] No
• [ ] Yes
  • [ ] Updated docs with SQL for downgrading the catalog

Metadata

Does this PR add a new Metadata feature?

• [X] No
• [ ] Yes
  • Does run_sql auto manages the new metadata through schema diffing?
    • [ ] Yes
    • [ ] Not required
  • Does run_sql auto manages the definitions of metadata on renaming?
    • [ ] Yes
    • [ ] Not required
  • Does export_metadata/replace_metadata supports the new metadata added?
    • [ ] Yes
    • [ ] Not required

GraphQL

• [X] No new GraphQL schema is generated
• [ ] New GraphQL schema is being generated:
  • [ ] New types and typenames are correlated

Breaking changes

• [X] No Breaking changes

• [ ] There are breaking changes:

  1. Metadata API

     Existing query types:

     • [ ] Modify args payload which is not backward compatible
     • [ ] Behavioural change of the API
     • [ ] Change in response JSON schema
     • [ ] Change in error code

  2. GraphQL API

     Schema Generation:

     • [ ] Change in any NamedType
     • [ ] Change in table field names

     Schema Resolve:-

     • [ ] Change in treatment of null value for any input fields

  3. Logging

     • [ ] Log JSON schema has changed
     • [ ] Log type names have changed