Externalize submit "Save changes" message

What does this MR do?

This MR externalizes submit "Save changes" message and changes incorrectly scoped to unscoped i18n strings

Note: gitlab.pot has no changes because the string "Save changes" already exists in gitlab.pot

How to setup and validate locally

1. Change locale
2. Start GitLab
3. Verify "Save changes" strings in submit buttons are translated to locale language in UI

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.