Move database migration docs

[trmartin4]

📔 Objective

As written, our SQL Code Style docs include mostly instructions on how to write migration scripts. This PR moves those best practices closer to where they're applicable - the database migration docs - and also formats the documentation with expanders for easier consumption.

Note that I left the SQL Code Style docs as-is. These will be expanded upon in #648, and I didn't want to cause merge conflicts there.

⏰ 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

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[github-actions]

Checkmarx One – Scan Summary & Details – 3d776b19-1c58-4443-b97b-2e9645ed1253

Great job! No new security vulnerabilities introduced in this pull request

[withinfocus]

We got deep into database documentation at #593 and it has a bunch of moves. I'd like to get that merged first.

[withinfocus]

My other organization-related PR has merged so should we take a fresh look here?

The base branch was changed.

[trmartin4]

@withinfocus I've updated these docs to incorporate your changes.

I also reached out to @mkincaid-bw because I think that his changes to the SQL Code Style doc will complement my changes very nicely; I've extracted all the migration-specific instructions into a separate doc, leaving the door open for more in-depth code style specific to SQL, which he's doing in #648.

Would it be preferable for me to undo the changes to the Code Style doc in my PR? I can do that before I open it for review, as what I put in there (https://restructure-sql-docs.contributing-docs.pages.dev/contributing/code-style/sql) is very basic and based on some recommendations given for one of our database changes.

[withinfocus]

I feel like these changes are SQL coding standards, not migration-writing ones. We should think of column additions, view recreations, etc. as just those standards and not focus on a specific usage. It would be ideal to me to have this in one document.