[Change Proposal] Allow empty changelogs on packages with stack-aligned versions

## Description

It would be great if there was a way for packages with versions that are aligned with the Stack to have empty changelogs or have a type of change `empty` so the `elastic-package` linting passes.
Many packages are likely to be forward looking when in development stages and are also likely to not have significant changes just after the version has been bumped.

## Why

`apm-server` (and I assume other packages too) have package versions that are aligned with the stack and are forward looking, such as `8.0.0` and `8.1.0` at the moment this issue was written.

In order to be able to commit an unreleased package without any changes, it would be great to relax the required changelog entry check to avoid adding changelog entries such as:

```yaml
- version: "8.1.0"
changes:
- description: REPLACE ME WITH ACTUAL CHANGE LOG
type: enhancement
link: https://github.com/elastic/apm-server/pull/1234
```

See https://github.com/elastic/apm-server/pull/6676#discussion_r753156605.