[WXP] Document how to change the availability status of context menu items

[samantharamon]

Note to the reviewer: Unified manifest updates will be made in a separate PR since this PR may be published before WXP public preview.

[learn-build-service-prod]

Learn Build status updates of commit 7d699eb:

💡 Validation status: suggestions

File	Status	Preview URL	Details
docs/design/disable-add-in-commands.md	💡Suggestion	View	Details
docs/design/add-in-commands.md	✅Succeeded	View
docs/design/contextual-tabs.md	✅Succeeded	View
docs/design/interface-elements.md	✅Succeeded	View
docs/develop/configure-your-add-in-to-use-a-shared-runtime.md	✅Succeeded	View
docs/toc.yml	✅Succeeded	View

docs/design/disable-add-in-commands.md

• Line 31, Column 24: [Suggestion: learn-site-link-broken - See documentation] Link '/javascript/api/requirement-sets/common/context-menu-api-requirement-sets' points to a learn site page that doesn't exist. Check the path or URL and update the link.
• Line 140, Column 13: [Suggestion: learn-site-link-broken - See documentation] Link '/javascript/api/office/office.contextmenuupdaterdata' points to a learn site page that doesn't exist. Check the path or URL and update the link.
• Line 143, Column 101: [Suggestion: learn-site-link-broken - See documentation] Link '/javascript/api/office/office.contextmenu#office-office-contextmenu-requestupdate-member(1)' points to a learn site page that doesn't exist. Check the path or URL and update the link.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit 352689e:

❌ Validation status: errors

Please follow instructions here which may help to resolve issue.

File	Status	Preview URL	Details
	❌Error		Details

• [Error: CannotMergeCommit] Cannot merge commit 352689e50aa3661d16b51a41d6c45668fbb39f17 in branch samramon-context-menu of repository https://github.com/OfficeDev/office-js-docs-pr into branch main (commit 85bae43e6e72a36c9035d0badc65eb760ef8f6fe). Please follow this documentation: https://help.github.com/articles/resolving-a-merge-conflict-using-the-command-line/ to use git.exe to resolve you content conflicts locally and then push to remote.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel