Add Service Lifecycle Support

[0xTim]

These changes are now available in 1.53.0

Adds support for Swift Service Lifecycle as we prepare Vapor for Vapor 5.

This allows you to add Databases to a ServiceGroup and have service lifecycle handle shutting down the connection pool when the application exits and provides a better integration with the ecosystem.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 24.35%. Comparing base (2c196f6) to head (9f3c2ee).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/FluentKit/Database/Databases.swift	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #646      +/-   ##
==========================================
- Coverage   24.36%   24.35%   -0.01%     
==========================================
  Files         148      148              
  Lines        8673     8676       +3     
==========================================
  Hits         2113     2113              
- Misses       6560     6563       +3     

Files with missing lines	Coverage Δ
Sources/FluentKit/Database/Databases.swift	0.00% <0.00%> (ø)

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[gwynne]

Suggested change

	try await gracefulShutdown()
	await self.shutdownAsync()
	do {
	try await gracefulShutdown()
	} catch is CancellationError {
	// ignore; we still need to shut down for sudden cancellation
	}
	await self.shutdownAsync()

[0xTim]

We probably want to trigger a shutdown for any error actually right? So a try? might be better.