[26.1 backport] context list: temporarily add ContextType to JSON output

[thaJeztah]

• backport cli/command/context: improve tests and add coverage for custom metadata in contexts #5097
• backport context list: temporarily add ContextType to JSON output #5094

Docker Desktop currently ships with the "cloud integration" wrapper, which outputs an additional ContextType field in the JSON output.

While this field is non-standard, it made its way into Visual Studio's Docker integration, which uses this to exclude "aci" and "eci" context types that are not supported by Visual Studio.

This patch;

• conditionally adds a ContextType field to the JSON output
• but ONLY when using the default "{{json .}}" or "json" formats (which are the formats used by Visual Studio)
• if the context is a "aci" or "eci" context, that type is preserved, otherwise the default "moby" type is used.

- Description for the changelog

Add a temporary `ContextType` field to the JSON output of "docker context ls" for backward-compatibility with Visual Studio.

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

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 61.35%. Comparing base (b72abbb) to head (258e274).

Additional details and impacted files

@@           Coverage Diff           @@
##             26.1    #5095   +/-   ##
=======================================
  Coverage   61.34%   61.35%           
=======================================
  Files         298      298           
  Lines       20688    20700   +12     
=======================================
+ Hits        12691    12700    +9     
- Misses       7096     7099    +3     
  Partials      901      901           

[thaJeztah]

Let's bring this one in