Add additional variables for Jenkins

[oscarhearsawho]

As a result of the Linear FS-2764, we identified that customers using a Jenkins & Bitbucket combo meal may need to include these additional variables in their Jenkins Pipeline:

• SEMGREP_REPO_NAME
• SEMGREP_REPO_URL
• SEMGREP_COMMIT

Specifically the commit one, without this PR comments were failing for the customer, due to a piece of logic we have in renderer.py that requires the repo_name, pr_id and commit to be able to post comments.

The definitions I've added (and the location of the addition) might need tweaking, definitely not a final version here.

[netlify[bot]]

✅ Don't forget to add /docs at the end of the deploy preview site URL!

Name	Link
🔨 Latest commit	2594b0ef1318a2ee5c5a5966b459862b96ae01ed
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😎 Deploy Preview	https://deploy-preview-2263--semgrep-docs-prod.netlify.app
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[armchairlinguist]

I think we need to make this change in more places, and provide more context on when and how to set which variables, so I'd advise we don't accept this PR as written but do use it as a foundation to improve here. Thanks for your contributions, Oscar!