[backend] Upgrade go chi to v5

[likawind]

Describe your changes and why you are making these changes

This PR upgrades go chi to latest version based on @vsreekanti 's comment: "We're currently using an 18-month old release of go-chi because we aren't using the go-modules-ed version of it. We should upgrade."

We refer to chi's official guide to use /chi/v5 and /chi/v5/middleware, changed all imports and updated go.mod and go.sum using go mod tidy.

Related issue number (if any)

ENG-1222

Checklist before requesting a review

Compiles. As long as in-PR test passed, it should be sufficient.

• I have created a descriptive PR title. The PR title should complete the sentence "This PR...".
• I have performed a self-review of my code.
• I have included a small demo of the changes. For the UI, this would be a screenshot or a Loom video.
• If this is a new feature, I have added unit tests and integration tests.
• I have run the integration tests locally and they are passing.
• I have run the linter script locally (See python3 scripts/run_linters.py -h for usage).
• All features on the UI continue to work correctly.
• Added one of the following CI labels:
  • run_integration_test: Runs integration tests
  • skip_integration_test: Skips integration tests (Should be used when changes are ONLY documentation/UI)

[cw75]

I'm glad that there doesn't seem to be any API changes required. :)