feat: automatic update version nr

[ahuininga-orisha]

Summary

• Replaced the hard-coded version string in etc/adminhtml/system.xml with a dynamic label field that reads the installed package version at runtime.
• Added Model/Config/Comment/Version.php, implementing Magento's CommentInterface, which uses ComposerInformation::getInstalledMagentoPackages() to look up the tweakwise/magento2-tweakwise-export composer package version and display it at the top of the Export settings group.
• The version label is now always in sync with the installed composer version — no more manual version bumps in XML.

How to test

Scenario 1 — Version is displayed in admin

1. Run setup:di:compile and cache:clean.
2. Log in to the Magento admin and navigate to Stores → Configuration → Catalog → Tweakwise → Export.
3. Verify that a "Module version" field is shown at the top of the group, displaying the correct version (e.g. Tweakwise Export version v7.8.3).

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Scenario 2 — Version matches composer

1. Run composer show tweakwise/magento2-tweakwise-export and note the installed version.
2. Compare it to what is shown in the admin field from Scenario 1.
3. Verify they match.

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