switch to miniconda image
References Issue https://code.ornl.gov/sns-hfir-scse/reflectometry/reflectometry/-/issues/247
Following the example of the data_workflow/Dockerfile.webmon, replace the CentOS 7 image with an miniconda image, and create a conda environment to run the web_reflectivity
service.
The current CentOS 7 image has a default SQlite database version is 3.7.15. However, the Django>3.0,<4.0 requirement means the SQlite database version must be >= 3.9.0 according to the Django documentation. This poses a problem that the conda environment aims to solve.