Support header nav to register nav control to farthest right

[Hailong-am]

Is your feature request related to a problem? Please describe.

Support header nav to register nav control to farthest right. For now, help Menu always be the farthest right.

<EuiHeaderSectionItem border="left">
    <HeaderNavControls navControls$={observables.navControlsRight$} />
  </EuiHeaderSectionItem>

  <EuiHeaderSectionItem border="left">
    <HeaderHelpMenu
      helpExtension$={observables.helpExtension$}
      helpSupportUrl$={observables.helpSupportUrl$}
      opensearchDashboardsDocLink={opensearchDashboardsDocLink}
      opensearchDashboardsVersion={opensearchDashboardsVersion}
      surveyLink={survey}
    />
</EuiHeaderSectionItem>

https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/public/chrome/ui/header/header.tsx#L230-L242

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[joshuarrrr]

@kgcreative I'd like a little more guidance here - we already have a lot of header nav entry points, and if we add a new one, even the naming will start to get confusing. Furthermore, what are the guiding design principles we'd like plugin authors to follow in terms of registering their nav item to the left or the right of the help menu? Is there some heuristic to follow?