fetch-configlet_v3: Support repo rename
fetch-configlet_v3: Support repo rename

This commit means that a local copy of this script will keep working
even after this repo is renamed from `configlet-v3` to `configlet`.

Changes:
- Add the `--location` flag to the curl command so that we follow
  redirects during the API request.
- No longer hard-code the filename of the asset.

Decisions:
- Don't use `jq` to parse the JSON. We shouldn't assume that the
  end-user has it installed. Let's use it only in the
  `exercism/github-actions` version of this script.
- Use `grep`, rather than `sed`, `awk` or pure bash. We try to maximise
  readability for the average maintainer.
- Try to maximise portability. For example, we avoid using grep's
  `-P, --perl-regexp` flag, which isn't available in e.g. OpenBSD's
  grep (see https://man.openbsd.org/grep).

exercism/configlet