clean up CI config docs and samples

[khorne3]

There are a lot of files in this PR, but here are the previews for the primary elements:

• Sample CI configurations
• Add Semgrep manually to CI providers
• All three Bitbucket/Jenkins-related docs in the KB have been consolidated into Run Semgrep in Jenkins when using Bitbucket as the source code manager
• Simplified Scan GitHub projects in Jenkins to include instructions for full and diff-aware scans
• Minor text edits to Create a Jenkins Shared Library for use with Semgrep scans
• No changes to the content in the following; they're just being moved from the primary CI integrations doc to the KB:
  • Add Semgrep to your Semaphore pipeline
  • Upload Semgrep CI findings to GitHub Advanced Security Dashboard
  • Upload Semgrep CI findings to GitLab Security Dashboard
• The /semgrep-supply-chain/setup-jenkins-ui.md doc and all references to it have been deleted, since this is no longer an issue that needs a workaround

Please ensure

• A subject matter expert (SME) reviews the content
• A technical writer reviews the content or PR
• Redirects are added if the PR changes page URLs
• If you have changed any header tag links (doc/#this-kind-of-anchor), update all instances of that link

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