review the usage of i18n on every entrypoint

[kaisecheng]

Relates: #14245

Logstash has a couple of entrypoints in bin/. One of the entrypoint bin/logstash-keystore experienced exception=NameError, message=>uninitialized constant I18n when it comes to the deprecation message. It is because the entrypoint does not load i18n

As a developer of Logstash, the goal is to be able to rely on i18n being loaded from any entrypoint. At this moment, other entrypoints could have the same issue.