api: disable old graphql endpoint by default

[mastercactapus]

• Identified the issue which this PR solves.
• Read the CONTRIBUTING document.
• Code builds clean without any errors or warnings.
• Added appropriate tests for any new functionality.
• All new and existing tests passed.
• Added comments in the code, where necessary.
• Ran make check to catch common errors. Fixed any that came up.

Description:
Defaults the /v1/graphql endpoint to be disabled (returning a 404) and decouples assignment.RawTarget from the old code.

[dctalbot]

NIT: should switch to use

function formatHeading(s = ''): string {
  return startCase(s)
    .replace(/\bTwo Way\b/, 'Two-Way')
    .replace('Enable V 1 Graph QL', 'Enable V1 GraphQL')
    .replace('Git Hub', 'GitHub')
    .replace(/R Ls\b/, 'RLs') // fix usages of `URLs`
}

EDIT: we'll fix this later