Add version requirement for B-Series to readme

ros2: Fix equal link frames for mono and stereo nodes in launch file

Add version requirement for C-Series to readme

CI: Bump tested Ensenso SDK to the latest version of the 3.4 branch

ensenso_camera: Fix timestamp on virtual marker object publisher

ensenso_camera: Fix finding of first available camera serial

The "BySerialNo" node has been hidden and linked to the "Cameras"
node, which also includes the two nodes "ByEepromId" and
"BySerialNo". When iterating over the items in the "Cameras" node, it 
could occur that the function tried to access the inexistent item 
"Available". The problem probably did not occur before, because the 
cameras are listed alphabetically and real cameras with numeric serial 
numbers are listed before the two nodes "ByEepromId" and "BySerialNo",
letting the function find and return a camera serial without causing
an exception.

We now check whether the item is a camera by requiring the
"Status/Available" node to be existing.

ensenso_camera_test: Remove SDK version check for S-series tests

Since we only support the last three Ensenso SDK versions and those three versions now all include S-series support, we can drop the dedicated check for the tests.

Bump version to 2.0.0

Bump version to 1.7.1

Bump version to 2.0.0