docs: add Bitbucket Data Center self-hosting setup

[svarlamov]

Summary

• add concise, mirrored Bitbucket Data Center setup guides for Helm and Docker Compose
• document the OAuth incoming link, least-privilege scope, service-account HTTP token, project webhooks, context paths, TLS/networking, and official local evaluation resources
• extend both task scm:configure flows, config examples, and doctor validation for bitbucket-datacenter
• update documentation indexes, prerequisites, troubleshooting, and provider references

Validation

• docker-compose: task doctor
• helm: task lint
• helm: task test:render
• exercised both interactive SCM wizards with a context-path Bitbucket Data Center URL and compared their generated configuration
• node --check for both SCM wizard scripts
• bash -n for both doctor scripts
• verified all new official Atlassian and Docker links return HTTP 200

The combined Helm task doctor was not run because kubectl is unavailable in the local environment; its Helm lint and render checks pass independently.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.