This fix tries to address the proposal raised in 28946
to support plugins in `docker inspect`.
The command `docker inspect` already supports
"container", "image", "node", "network", "service", "volume", "task".
However, `--type plugin` is not supported yet at the moment.
This fix address this issue by adding the support of `--type plugin`
for `docker inspect`.
An additional integration test has been added to cover the changes.
This fix fixes 28946.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
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