New Cheat sheet: AI_Agent_Security_Cheat_Sheet.md

[KadirArslan]

None of existing resources provide actionable security guidance specifically for agentic AI systems. So I created one.

For more details check the issue https://github.com/OWASP/CheatSheetSeries/issues/1925

I tried to keep "clean" this cheat sheet with using only simple action items. But I know example codes are seems huge. But IMO this is crucial to be understandable.

:triangular_flag_on_post: If your PR is related to grammar/typo mistakes, please double-check the file for other mistakes in order to fix all the issues in the current cheat sheet.

Please make sure that for your contribution:

• [X] In case of a new Cheat Sheet, you have used the Cheat Sheet template.
• [X] All the markdown files do not raise any validation policy violation, see the policy.
• [X] All the markdown files follow these format rules.
• [X] All your assets are stored in the assets folder.
• [X] All the images used are in the PNG format.
• [X] Any references to websites have been formatted as [TEXT](URL)
• [X] You verified/tested the effectiveness of your contribution (e.g., the defensive code proposed is really an effective remediation? Please verify it works!).
• [X] The CI build of your PR pass, see the build status here.

If your PR is related to an issue, please finish your PR text with the following line:

This PR fixes issue #1925 .

AI Tool Usage Disclosure (required for all PRs)

Please select one of the following options:

• [X] I have NOT used any AI tool to generate the contents of this PR.
• [ ] I have used AI tools to generate the contents of this PR. I have verified the contents and I affirm the results. The LLM used is [llm name and version] and the prompt used is [your prompt here]. [Feel free to add more details if needed]

Thank you again for your contribution :smiley: