feat: remove openapi-v3 from apiconnect dependencies

[bajtos]

Use @loopback/rest to access openapi-related types and helpers.

This pull request is a part of #5692.

BREAKING CHANGE: @loopback/core and @loopback/rest were moved to peer dependencies, to ensure the extension uses application's version of these modules. If this change breaks your application (which is unlikely), then simply add both @loopback/core and @loopback/rest to your project dependencies.

I am observing timeouts when running the tests locally (even on master), I think they are not related to my changes and will rely on CI builds to confirm.

Checklist

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• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

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[bajtos]

@raymondfeng thank you for the comment above. How to move this pull request forward? Are you fine with the proposed approach or would you like me to rework the patch to avoid introduction of peer dependencies? Something else?

[raymondfeng]

Here is my personal preference but I won't block you from merging this PR as is.

1. Simply remove @loopback/openapi-v3 without changing to peerDependencies in this PR.
2. Having a follow-up PR to universally switch to peerDependencies for all extension-like packages.

[bajtos]

1. Simply remove @loopback/openapi-v3 without changing to peerDependencies in this PR.
2. Having a follow-up PR to universally switch to peerDependencies for all extension-like packages.

That's a good plan 👍

I cannot simply remove @loopback/openapi-v3 from dependencies, I need to move @loopback/rest from dev-dependencies to regular dependencies to avoid the situation when import statement is referencing a dependency that is not available.

@raymondfeng LGTY now?