[Fix #8749] Disable Style/IpAddresses by default in gemfiles and gemspec files

[dvandersluis]

Fixes #8749.

Not sure if there's a way to test default exclusions so I didn't try to add tests for it but I am happy to if desired.

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

Looks good! Thanks!