feat(server): add custom start handler (backport #19854)

[mergify]

Description

Support custom starting app logic. This allows forks of the SDK only modifying the start command to only replace their start logic. Backport to v0.50 won't contain the api improvements (breakage) but will be additive only.

Use case:

Replace the need a forking the sdk for things like: release/v0.50.x...rollkit:cosmos-sdk:release/v0.50.x

How to use:

Set StartCommandHandler and AddFlags in StartCmdOptions when calling AddCommands.

Why method like startAPIServer, startGrpcServer or other private methods in start.go are not simply public to make creating StartCommandHandler less verbose?

Because we do not to provide any api guarantee for those functions. If you are re-implementing SDK's start command, you should know what you are doing and can reimplement those functions yourself.

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Author Checklist

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please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• reviewed "Files changed" and left comments if necessary
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• updated the relevant documentation or specification, including comments for documenting Go code
• confirmed all CI checks have passed

Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed all author checklist items have been addressed
• reviewed state machine logic, API design and naming, documentation is accurate, tests and test coverage

Summary by CodeRabbit

• New Features
  • Added customizability to the server's start command for enhanced flexibility.
• Changes
  • Streamlined server module operations by enabling callback into the application struct post-setup.
  • Simplified function calls in the building apps documentation by removing specific parameters.
  • Refactored server startup logic to improve code efficiency and error handling.
• Bug Fixes
  • Ensured consistency in the PreBlock function by adjusting its return type.
• Refactor
  • Removed outdated concepts such as basic manager and ModuleInitFlags to clean up the codebase.
  • Updated command addition functions to support new start command customization options.
  • Adjusted command initialization in the simulation application for clarity and efficiency.
• Documentation
  • Updated building apps documentation to reflect changes in function call parameters.

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This is an automatic backport of pull request #19854 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of def211d has failed:

On branch mergify/bp/release/v0.50.x/pr-19854
Your branch is up to date with 'origin/release/v0.50.x'.

You are currently cherry-picking commit def211d86.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   server/types/app.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md
	both modified:   UPGRADING.md
	both modified:   docs/docs/build/building-apps/05-app-testnet.md
	both modified:   server/start.go
	both modified:   server/util.go
	both modified:   simapp/simd/cmd/commands.go
	both modified:   simapp/simd/cmd/root.go
	both modified:   simapp/simd/cmd/root_v2.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally