Add versioning to PoST data directory via postdata_metadata.json file

[fasmat]

Description

This introduces versioning to PoST data (closes #210 ). The version is stored inside the postdata_metadata.json file. If no version is present Version 0 is assumed which will be migrated to version 1.

Version 1 has the following changes over Version 0:

• A missing NonceValue is added if Nonce is present.
• The ScryptParams that were used to generate the PoST data were added to the metadata file.

These additions allow changes to how the data is stored on disk and allow for smooth migrations from an older version of PoST to a newer version.

TODO:

• NodeId and CommitmentATX are now hex encoded instead of base64 (closes Make key handling more ergonomic #203 and closes inconsistent representation of commitment ATX and node ID #163); For this we would also need to update libpostrs @poszu

[codecov]

Codecov Report

Attention: Patch coverage is 52.40964% with 79 lines in your changes missing coverage. Please review.

Project coverage is 59.0%. Comparing base (50539ea) to head (1a97f90).

Files with missing lines	Patch %	Lines
initialization/migrate_metadata.go	55.5%	38 Missing and 14 partials ⚠️
shared/post_metadata.go	17.2%	22 Missing and 2 partials ⚠️
initialization/initialization.go	81.2%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #211     +/-   ##
=========================================
- Coverage     59.8%   59.0%   -0.9%     
=========================================
  Files           30      31      +1     
  Lines         2291    2407    +116     
=========================================
+ Hits          1372    1421     +49     
- Misses         781     835     +54     
- Partials       138     151     +13     

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