Changed default value of server.maxPayloadBytes in documentation

[perrinal]

Summary

As described in #31974 the server.maxPayloadBytes in now 25MB

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
  - [ ] Documentation was added for features that require explanation or tutorials
  - [ ] Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-docs (Team:Docs)

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 9355de1

[gchaps]

@perrinal Thanks for helping with the docs! This PR requires a release note label, so I added release_note:skip. We use this label for our docs PRs. This label tells our script not to include this PR in the Release Notes.

[n0othing]

Based on #49218 (comment), the increase in #31974 doesn't apply to the global server.maxPayloadBytes (which still defaults to 1048576)

[perrinal]

@gchaps how to stop this PR as I misinterpreted the PR and the doc was correct before.