Run bundle size analysis only when frontend files are changed

What does this MR do?

Prevents the webpack bundle-size-analyzer from running in contexts where it is not needed. This rule will configure it to run only when files are changed which might have an impact on webpack bundle sizes.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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Security

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closes: gitlab-org/frontend/playground/webpack-memory-metrics#17 (closed)