Improve first contribution docs

Changelog: changed

Because any maintainer can merge
Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/397788

This commit updates and renames the screenshots

Because we're changing how we
update pages in this folder

Refactored MR Review section

Added Pipeline Test section

Applied suggested changes to the Pipeline section

Improved the Docs and reworded the line 352

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Apply 7 suggestion(s) to 1 file(s)

Making sure that sentences appear in a single line to make suggestions & contributions easier later

Apply 4 suggestion(s) to 1 file(s)

Apply 1 suggestion(s) to 1 file(s)

Because we have scraps of
disparate info and we need
an easy friendly guide.

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/744