Update gitignore to ignore IntelliJ related files

[kota2and3kan]

Description

This PR updates the .gitignore file to untrack IntelliJ related files.

Please take a look!

Related issues and/or PRs

N/A

Changes made

• Added IntelliJ related files to the .gitignore file.

Checklist

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

N/A

[brfrn169]

LGTM! Thank you!

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[feeblefakie]

LGTM! Thank you!