[PM-18448] self-host: support other external database providers

[dionysius]

📔 Objective

Support other external database providers supported by bitwarden server: https://github.com/bitwarden/server/blob/main/src/Admin/Startup.cs#L50-L68

Optimally we would reorganise the values.yaml's database property to make navigating it a bit cleaner. But the current implementation uses minimal changes and is backwards-compatible even if databaseProvider is missing. There may be a way to simplify {{- if eq "sqlserver" (default "sqlserver" .Values.databaseProvider) }}.

In my opinion supported provider sqlite doesn't make much sense in a helm managed kubernetes environment though it is technically almost possible with the current PR (missing volume setup) - hence not documented and the focus being external servers.

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[CLAassistant]

All committers have signed the CLA.

[bitwarden-bot]

Thank you for your contribution! We've added this to our internal Community PR board for review.
ID: PM-18448