Write out the data for a deciles chart

[ccunningham101]

Instead of (or in addition to) outputting a decile chart image, the action could output the deciles table (the first step of decile chart generation). This could allow for the following:

1. Help address Cannot always reconstruct denominator and group_by parameters #17
2. Allow for redaction and output checking to happen on the relevant data table
3. Offline and off-server plotting that could occur without the output checking loop (following Will's workflow)

The action could use a flag to determine whether to return data, graphics, or both

[iaindillingham]

Do you have any thoughts about configuration, @ccunningham101? #24 added the mechanism for reading JSON-encoded configuration. I feel we should use this (i.e. config), rather than arguments (e.g. --input-files), to specify whether we'd like deciles-charts to write tables, charts, or tables and charts. This is because I feel JSON-encoded configuration is for optional things, whereas arguments are for required things. How does the following look, to you:

generate_deciles_charts:
  run: >
    python:latest analysis/deciles_charts.py
      --input-files output/measure_*.csv
      --output-dir output
  config:
    output:
      - tables
      - charts
  needs: [generate_measures]
  outputs:
    moderately_sensitive:
      tables: output/deciles_table_*.csv
      charts: output/deciles_chart_*.png

I envisage that we'll add configuration and, eventually, decide to refactor how the config key looks. However, it would be good to keep existing configuration in mind when adding new configuration. Existing configuration is described in README.md.

[ccunningham101]

The specification above looks good to me!
I like the split of required params as arguments and options parameters with defaults in the config