Added a Block Config separate from Mining Config to reduce PoS confusion (issue #4836)

[OlegJakushkin]

Resolves #4836
The issue was that Mining.Enabled (that is extremely rarely used) made a user confused if it is needed to have the ability to set other Block creation parameters. With this PR, we enable Block parameters configuration separate from Mining parameter(s).
Backward compatibility and synchronisation are enabled on the MigrateConfigs step.

In other words, one might set, for example, Mining.Enabled, Mining.RandomizedBlocks, Blocks.RandomizedBlocks Blocks.ExtraData at the same time and:

1. If RandomizedBlocks is the same on Mining and Blocks continue, otherwise get an exception
2. Have properties in the Mining and Blocks configurations synchronised

Changes:

• Added separate Block creation configuration settings
• Deprecated them in the Mining configuration by adding relevant descriptions
• Made config synchronisation step (based on an existing implementation)

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Other (please describe):

Testing

Added unit tests to test functionality as it is mostly cosmetic

• Yes
• No

In case you checked yes, did you write tests?

• Yes
• No

[smartprogrammer93]

Minor comments. Otherwise looks good.