`AdaptCmd` was previously checking for a `.WithCancel` suffix
on context strings, however it's possible for a context to be
cancellable without ending in that suffix, such as when
`context.WithValue` was called after `WithContext`, e.g.:

```go
context.Background.WithCancel.WithValue(type trace.traceContextKeyType,
val <not Stringer>).WithValue(type api.DryRunKey, val <not Stringer>)
```

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

Previously, if a long-lived plugin process (such as
an execution of `compose up`) was running and then
detached from a terminal, signalling the parent CLI
process to exit would leave the plugin process behind.

To address this, changes were introduced on the CLI side
(see: docker/cli#4599) to enable
the CLI to notify a running plugin process that it should
exit. This makes it so that, when the parent CLI process
is going to exit, the command context of the plugin
command being executed is cancelled.

This commit takes advantage of these changes by tapping into
the command context's done channel and using it to teardown
on an up.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>