[feat]: add footer for SidebarInset

[maru7777]

Feature description

sometimes we may want to add a fix component at the very bottom of SidebarInset in Sidebar component. for example user input prompt area. If we have such a container at the very bottom of SidebarInset , which is similar as footer in sidebar provider, that really help

Affected component/components

No response

Additional Context

Additional details here...

Before submitting

• I've made research efforts and searched the documentation
• I've searched for existing issues and PRs

[maru7777]

and one more thing, can we add standalone button ,which can be use to control right sidebarpanel ? now we can only control left one.
history issues
#5651
#8868