en: replace master and slave with leader and follower

[saghevli]

Review the Contributing Guidelines

Before submitting a pull request, verify it meets all requirements in the Contributing Guidelines.

Translations

See the Contributing Guidelines. Verify you've:

• Tagged the language maintainer
• Prefixed the title with a language code
  • Example: "ja: Fix ..."

[Lily418]

Just wanted to share some related PR #217 where some resourses and discussion was collected.

#397 issue was closed before #217 was merged and perhaps could be reopened.

[doreensacker]

Hi there! I was just wondering if this can be merged?
It was kind of bothering me and I was happy to see that there is already an open PR about it :)