Add compose override editing support

[eliasfloreteng]

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Description

Adds an editor for compose override files (see https://docs.docker.com/compose/how-tos/multiple-compose-files/merge/) if there is one in the directory of the stack. It will appear above the editor for the normal compose file. It does not appear in the create menu, only when editing and if the file exists.

This is the second most requested feature in the discussions: #278 and #415

Type of change

• User interface (UI)
• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)