filebeat/module/apache: Rename the field `apache2.module.error` to `apache.module.error`

[herrBez]

Proposed commit message

Rename field apache2.module.error to apache.module.error in the Dashboard

Checklist

• [x] My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

None

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• #39480

Use cases

Screenshots

The original saved search uses apache2.error.module, while the correct field apache.error.module (added by me) shows that it is actually populated with a meaningful value.

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