feat(cli): Add feature flag and CLI parameters for Nano Contracts

[msbrogli]

Motivation

Add a feature flag and CLI parameters to run a localnet with NanoContracts enabled. These changes are temporary but they are useful to allow beta testers to experiment with Nano Contracts.

The activation of Nano Contracts for both mainnet and testnet will occur through the Feature Activation. The proper configuration will take place in a future PR.

Acceptance Criteria

1. Add a protection to prevent enabling Nano Contracts on any network except nano-testnet.
2. Add the CLI parameters --nano-testnet that will run the full node on a localnet.
3. Set nano-testnet to use the same version bytes as the testnet but different genesis.
4. Add feature flag ENABLE_NANO_CONTRACTS which is disabled by default except on the nano-testnet.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[jansegre]

Looks good to me, just looks like some tests that check for the settings have to be updated. Also, nano_testnet.yml does not have a .py module counterpart, I think it's fine tho, I'll open a PR to remove those (done, #942), since they have been deprecated for a while now.

[msbrogli]

Looks good to me, just looks like some tests that check for the settings have to be updated. Also, nano_testnet.yml does not have a .py module counterpart, I think it's fine tho, I'll open a PR to remove those (done, #942), since they have been deprecated for a while now.

Fixed!

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (3ce172f) 85.34% compared to head (a7cf1ba) 85.31%.

Files	Patch %	Lines
hathor/conf/settings.py	50.00%	4 Missing and 1 partial ⚠️
hathor/builder/cli_builder.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #941      +/-   ##
==========================================
- Coverage   85.34%   85.31%   -0.04%     
==========================================
  Files         290      291       +1     
  Lines       22511    22526      +15     
  Branches     3388     3391       +3     
==========================================
+ Hits        19212    19217       +5     
- Misses       2628     2634       +6     
- Partials      671      675       +4     

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