Deprecate getJSONFixture

What does this MR do and why?

• Deprecate getJSONFixture with a notice to use import
• Disable eslint import/no-deprecated rule on remaining uses of getJSONFixtures that are not yet changed:
  • dynamic file paths in cycle analytics fixtures
  • calls with a static path
• Remove global getJSONFixture so import/no-deprecated can correctly detect problems. A global call is not linted.

Related to #339346 (closed)

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.