Write two example notebooks to showcase EOPF Julia plugin and plotting the data

[felixcremer]

We could think about following one of the other example notebooks and convert the access into Julia.
Need to clarify whether other work packages would also provide example notebooks in Julia.

[konstntokas]

To publish the notebook on the notebook gallery, follow these steps:

• create a note book following the contribuion guidelines and create a PR to https://github.com/EOPF-Sample-Service/eopf-sample-notebooks. Once merged it will automatically published on https://eopf-sample-service.github.io/eopf-sample-notebooks/
• The notebook shall be able to be run on the JupyerHub as explained on the main page of the notebook gallery. Therefore, the Julia reader must be added to the default image. To do so, please write an issue to https://github.com/EOPF-Sample-Service/eopf-container-images/issues as it is done here and tag @rtmiz as reviewer: add xcube-eopf==0.1.1 EOPF-Sample-Service/eopf-container-images#11. You may indicate some information how to install the Julia reader.

@felixcremer

[felixcremer]

We should follow this notebook along: https://eopf-sample-service.github.io/eopf-sample-notebooks/introduction-xarray-eopf-plugin/