Update connect scm instructions and improve readability

[s-santillan]

Thanks for improving Semgrep Docs 😀

Please ensure

• A subject matter expert (SME) reviews the content
• A technical writer reviews the content or PR

This is an expansion of the original request.

• The doc seems long because we have instructions per-provider. I opted to use tabs for this, especially because users don't need to see all the instructions, just those for their provider.
• The UI changed so the steps changed. In particular:
  • Source Code Manager, Source Code Organizations are now all Source code managers
  • We now show all the SCMs under a drop-down box.
• Clarified a bit about choosing accounts to install SCMs on because some folks may wonder "where did the other accounts come from?"
• Removed some screenshots that change a lot, but did add the screenshot for viewing all accounts/orgs in a Semgrep deployment, because sometimes it's hard to visualize.

[netlify]

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

Name	Link
🔨 Latest commit	0a8e24a
🔍 Latest deploy log	https://app.netlify.com/sites/semgrep-docs-prod/deploys/67ae4fe8a4f67d00087374f3
😎 Deploy Preview	https://deploy-preview-1970--semgrep-docs-prod.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

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