feat: update base gas price on solo

[darrenvechain]

Description

This PR sets the base gas price for solo in the first block. It is instantly mined in the first block so the genesis remains unaffected.

VET Transaction:

• Solo (Before change): 21 VTHO
• Testnet: 0.21 VTHO
• Solo (With changes): 0.21 VTHO

Type of change

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] New and existing E2E tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 59.45946% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 61.62%. Comparing base (b83a007) to head (458df05). Report is 7 commits behind head on master.

Files	Patch %	Lines
cmd/thor/solo/solo.go	59.45%	9 Missing and 6 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #722 +/- ## ========================================== + Coverage 61.25% 61.62% +0.37% ========================================== Files 194 194 Lines 18207 18259 +52 ========================================== + Hits 11152 11252 +100 + Misses 5973 5908 -65 - Partials 1082 1099 +17 ```

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[darrenvechain]

Hey @libotony I made 2 commits to resolve PR comments