[chore] add text about unmaintained vendor components (#11616)

#### Description

This PR adds language to our definition of `unmaintained` that allows
vendor-specific components to become unmaintained if they lose an active
code owner from the contributing vendor. This is necessary to prevent a
vendor-specific component form being maintained only by the community
instead of by the vendor. Since vendors had privileged access to getting
components accepted in contrib they must be held to a higher standard
for maintaining those components.

---------

Co-authored-by: Alex Boten <223565+codeboten@users.noreply.github.com>
Co-authored-by: Pablo Baeyens <pbaeyens31+github@gmail.com>

docs/component-stability.md

@@ -73,3 +73,8 @@ The component is planned to be removed in a future version and no further suppor
 ### Unmaintained
 
 A component identified as unmaintained does not have an active code owner. Such component may have never been assigned a code owner or a previously active code owner has not responded to requests for feedback within 6 weeks of being contacted. Issues and pull requests for unmaintained components will be labelled as such. After 3 months of being unmaintained, these components will be removed from official distribution. Components that are unmaintained are actively seeking contributors to become code owners.
+
+Components that were accepted based on being vendor-specific components will be marked as unmaintained if
+they have no active code owners from the vendor even if there are other code owners listed. As part of being marked unmaintained, we'll attempt to contact the vendor to notify them of the change. Other active code
+owners may petition for its continued maintenance if they want, at which point the component will no
+longer be considered vendor-specific.