Use shell builtin `command -v` instead non-standard `which`

What does this MR do?

This MR improves the consistency and maintainability, robustness of shell scripts in GitLab projects

This was originally something doing in gitlab-foss!31014 (comment 225759258), as @rpaik asked here(gitlab-foss!31014 (comment 225759258)), I'd like to continue shell script refactoring, but I can't comment there, so directly send another MR in the new repository, and separate different items into different MR, to minimize the effort on resolving conflicts.

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

/cc @godfat for reviewing, thanks!