The tab in which to open the side panel. If the corresponding tab has
a tab-specific side panel, the panel will only be open for that tab.
If there is not a tab-specific panel, the global panel will be open in
the specified tab and any other tabs without a currently-open tab-
specific panel. This will override any currently-active side panel
(global or tab-specific) in the corresponding tab. At least one of this
or windowId must be provided.
The window in which to open the side panel. This is only applicable if
the extension has a global (non-tab-specific) side panel or
tabId is also specified. This will override any
currently-active global side panel the user has open in the given
window. At least one of this or tabId must be provided.