DOCS-1699 - Remove auto-refresh requirement from external dashboard sharing

[JV0812]

Purpose of this pull request

This pull request updates the Share a Dashboard Outside Your Organization doc to decouple the auto-refresh requirement from external sharing. Specifically:

• Removed the statement that auto-refresh must be enabled to share a dashboard outside the organization
• Removed the backfill caveat (no longer applicable since auto-refresh is not required)
• Updated the unauthenticated viewers restriction to remove the reference to "auto-refresh enabled as well as"
• Retained the note that panels incompatible with auto-refresh will only show data for logged-in viewers (still accurate — auto-refresh can still be used, it's just no longer required)

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

https://sumologic.atlassian.net/browse/DOCS-1699

[kimsauce]

Looks great! Welcome back, @JV0812 !