add generate_graph.sh

This commit introduces a script that parses update markdown and displays a plot via gnuplot

$ ./tools/generate_graph.sh -h
usage: ./tools/generate_graph.sh -t -p

This script creates a gnuplot by parsing the markdown from within 'docs'

OPTIONS:

  -t        include testing updates
  -p        include prod updates
  -d        distributions (cc7,c8,cs8). default is 'all'
  -s        filter start date (YYYYMMDD). default is to not filter
  -e        filter end date (YYYMMDD). default is to not filter
  -x        exclude number of packages over this figure
  -h        display this help

As an example, the following would create a graph similar to the below ./tools/generate_graph.sh -t -s 20210101 -x 1000