Add initial nimbus implementation

[stdevMac]

Changes:

• Add a initial nimbus implementation for consensus, validator and import and key exporter.

Types of changes

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

Testing

Requires testing

• [x] Yes

In case you checked yes, did you write tests?

• [x] Yes

Should be run also a validator using our stack with nimbus

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 11.94969% with 140 lines in your changes missing coverage. Please review.

Project coverage is 25.31%. Comparing base (fdd677d) to head (67aa676).

Files with missing lines	Patch %	Lines
cli/actions/importKeys.go	1.81%	106 Missing and 2 partials :warning:
cli/actions/slashing.go	25.92%	16 Missing and 4 partials :warning:
cli/importKeys.go	45.45%	4 Missing and 2 partials :warning:
internal/pkg/clients/types.go	0.00%	4 Missing :warning:
cli/generate.go	33.33%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #388      +/-   ##
===========================================
- Coverage    25.45%   25.31%   -0.15%     
===========================================
  Files          119      119              
  Lines        18045    18192     +147     
===========================================
+ Hits          4594     4605      +11     
- Misses       12929    13059     +130     
- Partials       522      528       +6     

Flag	Coverage Δ
unittests	25.31% <11.94%> (-0.15%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[stdevMac]

474226e

Fixed here https://github.com/NethermindEth/sedge/pull/388/commits/474226e67863df7eca7ef48334c04263d776f1b6