Add nessai to containers

This merge request ads nessai to the template used to generate the docker files which is needed for the tests to pass for !921 (merged).

I've regenerated the docker files for each python version using the included script write_dockerfiles.py

containers/dockerfile-template

@@ -34,7 +34,7 @@ RUN pip install sphinx numpydoc nbsphinx sphinx_rtd_theme sphinx-tabs autodoc
 
 # Install dependencies and samplers
 RUN pip install corner lalsuite theano healpy cython tables
-RUN pip install cpnest dynesty emcee nestle ptemcee pymc3 kombine dnest4
+RUN pip install cpnest dynesty emcee nestle ptemcee pymc3 kombine dnest4 nessai
 RUN conda install -n ${{conda_env}} -c conda-forge pymultinest ultranest
 
 # Install Polychord