chore: Add explicit return type for most functions

[lym953]

What does this PR do?

Add explicit return type for most functions.

Not adding return type for functions whose return type is too long, e.g.

function findSubscriptionsInTemplate(resources: Resources): {
    key: string;
    subscriptionResource: {
        Type: string;
        Properties: any;
    };
}[] {
  ...
}

Motivation

To make code easier to understand.

Testing Guidelines

npm test can still pass.

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog

[datadog-datadog-prod-us1]

⚪ Code Quality Violation

Unexpected any. Specify a different type. (...read more)

Do not use the any type, as it is too broad and can lead to unexpected behavior.

    

[datadog-datadog-prod-us1]

⚪ Code Quality Violation

Unexpected any. Specify a different type. (...read more)

Do not use the any type, as it is too broad and can lead to unexpected behavior.