Add back 1.8 jar and add new 2.0 OBS jar

[LuQQiu]

Add back OBS 1.8 jar and add new 2.0.0 jar

[LuQQiu]

@madanadit In previous PR, I mistakenly delete the 1.8 jar. I add back the 1.8 jar and add the new 2.0 jar. PTAL ,thanks

[madanadit]

@LuQQiu the target directory should not be there. we should not add it back

[LuQQiu]

@madanadit Any preference for where to put the OBS jar? AWS or some directory in this repo?

[madanadit]

@LuQQiu why do we need to publish the jar at all?

[LuQQiu]

@madanadit In the OBS docs, we have

OBS under storage is implemented as an under storage extension. A precompiled OBS under storage jar 
can be downloaded from [here](https://github.com/Alluxio/alluxio-extensions/tree/master/underfs/obs/target).

We want to give the users pre-compiled jar which users can directly download and install in their Alluxio.

[madanadit]

you can remove that statement from the doc