Don't allow core id to be set manually

[gerrycampion]

This update does not allow an author to manually set Core.Id to a valid id.
If a rule is saved and the core id:

• matches the core id pattern
• does not match the previous saved core id

then the core id is replaced by empty string.

You can test this by creating new rules or modifying existing rules with valid and invalid core ids. A valid core id matches the pattern /^CORE-\d{6}$/

[github-actions[bot]]

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[nhaydel]

This issue is good to close.

Tested by manually assigning a valid rule id and having it overwritten to an empty string on save. Manually assigned an invalid rule id and it was not overwritten