Add support for --compat-auth-file in login/logout

This mostly just inherits the c/common/pkg/auth implementation,
except that AuthFilePath and DockerCompatAuthFilePath can not be set
simultaneously, so don't unnecessarily explicitly set AuthFilePath.
c/common already handles that.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

docs/source/markdown/podman-login.1.md.in

@@ -32,6 +32,10 @@ For more details about format and configurations of the auth.json file, see cont
 
 @@option cert-dir
 
+#### **--compat-auth-file**=*path*
+
+Instead of updating the default credentials file, update the one at *path*, and use a Docker-compatible format.
+
 #### **--get-login**
 
 Return the logged-in user for the registry.  Return error if no login is found.

docs/source/markdown/podman-logout.1.md.in

@@ -27,6 +27,10 @@ Remove the cached credentials for all registries in the auth file
 
 @@option authfile
 
+#### **--compat-auth-file**=*path*
+
+Instead of updating the default credentials file, update the one at *path*, and use a Docker-compatible format.
+
 #### **--help**, **-h**
 
 Print usage statement