feat: Add idempotency header to request for new sessions

[laolubenson]

closes #403

Change list

Please provide briefly described change list which are you going to propose.

Types of changes

What types of changes are you proposing/introducing to .NET client?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New feature (non-breaking change which adds value to the project)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Details

• Added method to modify/add "X-Idempotency-Key" request header before the HTTP request to the remote server is made
• lint AppiumCommandExecutor

Please provide more details about changes if it is necessary. If there are new features you can provide code samples which show the way they
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