refs platform/3262: upgrade gitlab agent helm chart to 2.8.3

[andypanix]

PR Type

Enhancement

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Description

• Upgraded the GitLab agent Helm chart default version from 2.8.2 to 2.8.3
• Updated CHANGELOG.md with version 0.9.0 release notes
• Added comparison link with previous version in changelog

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Changes walkthrough 📝

	Relevant files
Configuration changes	variables.tf Update GitLab agent Helm chart version                                      variables.tf Updated the default version of gitlab-agent Helm chart from 2.8.2 to 2.8.3 +1/-1
Documentation	CHANGELOG.md Add changelog entry for version 0.9.0                                        CHANGELOG.md Added entry for version 0.9.0 Documented upgrade of default Helm chart to version 2.8.3 +8/-0

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[sparkfabrik-ai-bot]

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