tools: Block Generator - allow exporting to files

[tzaffi]

Block Generator in File Exporting Mode + README + Makefile + Remove Python Runner

Functional changes

• tools/block-generator/generator/server.go - adding some calling context in maybeWriteError()
• allow exporting blocks into conduit's data directory. This is useful for generating Conduit fixtures. In particular:
  • tools/block-generator/runner/run.go - handle file exporting with a new conduit.yml template
  • tools/block-generator/runner/runner.go - don't enforce the need for a connection string in the case of a file exporter

Non functional changes:

• New Makefile targets:
  • make pg-up - standalone docker run
  • make pg-query - query postgres (handy since the DB credentials are variables of the Makefile)
  • make run-file-exporter - runner command tailored for file system exporting
  • make benchmark-blocks-export - encapsulates the previous to create blocks with a top-level report directory named according to the scenario
• Update the README with an explanation of the statistical distribution of block generator scenarios
• Slight rewording of the runner and daemon's help outputs
• Remove the python runner - all its previous functionality can be achieved with make targets

[codecov]

Codecov Report

Merging #5714 (316ff04) into master (02b99bb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5714   +/-   ##
=======================================
  Coverage   55.54%   55.54%           
=======================================
  Files         476      476           
  Lines       66853    66853           
=======================================
  Hits        37131    37131           
- Misses      27193    27201    +8     
+ Partials     2529     2521    -8     

see 12 files with indirect coverage changes

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[winder]

Looks pretty good overall.