Safer in-place migration handling

[todvora]

• Migration check for node.lock to prevent parallel run of a native opensearch and the datanode opensearch
• Safer preflight config result handling, without call side effects

Motivation and Context

Make the in-place migration more resilient.

How Has This Been Tested?

Manually + added unit tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[moesterheld]

Unfortunately, this does not really cover the first use case to prevent the parallel run.
The check checks if the lock file is writable, which in my test is the case and starts up data node.
Also, putting this in preflight will probably prevent data node from starting up altogether even though we might want it to start up for configuring it for migration and doing the compatibility check. The check should be placed at OS startup, or better, as a guard into the migration wizard.