Shorten URLs in searches by deleting UTF-8 param from any forms

What does this MR do?

Avoids to enforce UTF-8 in any forms, and then we will get shorter URLs, (a little bit) small HTML files, by removing utf8=%E2%9C%93 from all URLs and forms.

config/initializers/new_framework_defaults_6_0.rb, missed in !19891 (merged), is also introduced.

False positive from Danger

The following error from Danger is a false-positive, which will be avoided after gitlab-org/gitlab-dangerfiles!44 is released in the future release:

Use full URLs instead of short references (#123 (closed) or !123 (merged)), as short references are displayed as plain text outside of GitLab. For more information, take a look at our Commit message guidelines.

Screenshots (strongly suggested)

See the address bar.

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
  • !62823 (merged) (docs) and !62824 (merged) (Issue/MR templates)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• 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.

Related to #332246 (closed)