[healthcheck] preserve arguments with spaces in healthcheck test

[MayorFaj]

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Does this PR introduce a user-facing change?

Fixed healthcheck arguments containing spaces being incorrectly split when creating containers via Docker-compatible API 

Summary
Healthcheck arguments containing spaces were being incorrectly split when creating containers via the Docker-compatible API.

Problem

When using docker-compose or the Docker API to create containers with healthchecks, arguments with spaces were being split incorrectly:

# Input
healthcheck:
  test: ["CMD", "/usr/bin/mysql", "--execute=SELECT 1;"]

# What was stored (broken)
["CMD", "/usr/bin/mysql", "--execute=SELECT", "1;"]

# What should be stored (fixed)
["CMD", "/usr/bin/mysql", "--execute=SELECT 1;"]

Fixes #26519