Enforce UTF-8 encoding for errors coming from the Gitaly

What does this MR do and why?

Contributes to #421563 (closed)

Problem

Errors returned from Gitaly are encoded in ASCII. If the error message contains non-ASCII characters, then it returns an encoding error.

Solution

Encode Gitaly error messages in UTF-8.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

• Create a new project.
• Go to Settings > Repository > Push rules > Require expression in commit messages and configure the following regular expression: ^(¯\\_\(ツ\)_\/¯).
• Try to make a new commit via Edit single file and specify commit message not matching the expression (anything besides ¯\_(ツ)_/¯). Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.