Small improvements to UpdatePagesConfigurationService

What does this MR do?

This MR makes a few small improvements to UpdatePagesConfigurationService.

1. Don't bother returning the :reload field on success because it was only used by tests, and even there it was superfluous. Removing this reduces cognitive complexity.
2. Submit errors to Sentry. Before this MR they were being dropped silently. After this MR errors still get ignored but we can at least see how often they happen.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team