backports;

• daemon/config: clean up tests to use common helper #44773
• daemon/config: support alternate (common) unicode encodings using a BOM  #44790

• Stacked on top of daemon/config: clean up tests to use common helper #44773
• Follow-up to daemon/config: ignore UTF-8 BOM in config JSON #44770

- What I did
Instead of merely stripping a UTF-8 BOM, interpret UTF-8 and UTF-16 BOMs in order to support the common encodings on Windows.

This is a pragmatic but impure choice, in order to better support the default tools available on Windows Server, and reduce user confusion due to otherwise inscrutable-to-the-uninitiated errors like the following:

invalid character 'þ' looking for beginning of value
invalid character 'ÿ' looking for beginning of value

While meaningful to those who are familiar with and are equipped to diagnose encoding issues, these characters will be hidden when the file is edited with a BOM-aware text editor, and further confuse the user.

- How I did it

• https://pkg.go.dev/golang.org/x/text/transform
• https://pkg.go.dev/golang.org/x/text/encoding
• https://pkg.go.dev/golang.org/x/text/encoding/unicode

- How to verify it
Unit tests

- Description for the changelog

• Moby now supports UTF-16 encoded JSON configuration when a byte order mark is present
• Moby will report invalid UTF-8 in the JSON configuration early and comprehensibly

- A picture of a cute animal (not mandatory but encouraged)