Add database analysis and monitoring gems

[david-yz-liu]

Proposed Changes

(Describe your changes here. Also describe the motivation for your changes: what problem do they solve, or how do they improve the application or codebase? If this pull request fixes an open issue, use a keyword to link this pull request to the issue.)

This PR adds three gems to help with database analysis and monitoring:

• active_record_doctor, which performs static analysis checks on our database and application code
• annotaterb, which annotates models with database schema information. (I also used it to annotate our routes.rb file.)
• pghero, which provides a dashboard for database monitoring. I've enabled this dashboard for admin users only.

Screenshots of your changes (if applicable)

Associated documentation repository pull request (if applicable)

Type of Change

(Write an X or a brief description next to the type or types that best describe your changes.)

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)	X

Checklist

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Before opening your pull request:

• I have performed a self-review of my changes.
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  • Check that all changes are relevant to the purpose of this pull request, as described above.
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Questions and Comments

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[coveralls]

Pull Request Test Coverage Report for Build 23090402840

Details

• 8 of 10 (80.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 91.675%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
config/initializers/pghero.rb	6	8	75.0%

Totals
Change from base Build 22959769972:	0.006%
Covered Lines:	45077
Relevant Lines:	48357

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💛 - Coveralls