fix order of mta extensions for extension-descriptor-different-environments example

[cschuerings]

The extension-descriptor-different-environments example is currently not working as two extensions prod.mtaext and prod-scale-vertically.mtaext extend the same ID my-mta and hence the order can not be determined.

Running cf deploy -f -e prod.mtaext,prod-scale-vertically.mtaext shows the following logs:

Using extension descriptor with ID: "my-mta-prod"
Provided but unused extension descriptors because extend another MTA ID or extends order is not correct: [my-mta-prod]
Detected MTA schema version: "3"
Detected deployed MTA with ID "my-mta" and version "1.0.0"
Detected new MTA version: "1.0.0"
Deployed MTA version: "1.0.0"

Currently:

• my-mta-prod -> my-mta
• my-mta-prod-scale-vertically

This PR contains a fix, which specifies the order of extensions as follows:

• my-mta-prod-scale-vertically -> my-mta-prod -> my-mta

Hint: The fix is already mentioned in the corresponding readme for the example.

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[IvanBorislavovDimitrov]

Thank you very much for the fix!