Solve a nil pointer dereference of `ecdsaAllowList` in `boulder-ca` by
calling `reloader.New()` in constructor `ca.NewECDSAAllowListFromFile`
instead.
- Add missing entry `ECDSAAllowListFilename` to
`test/config-next/ca-a.json` and `test/config-next/ca-b.json`
- Add missing file ecdsaAllowList.yml to `test/config-next`
- Add missing entry `ECDSAAllowedAccounts` to `test/config/ca-a.json`
and `test/config/ca-b.json`
- Move creation of the reloader to `NewECDSAAllowListFromFile`
Fixes#5414
Samantha