[DataAvailability] introduce api package in access engine

[illia-malachyn]

Access node has 2 main responsibilities:

• serve data to end users
• gather data from protocol

I created the api package to encapsulate all the logic related to serving data into 1 package. I think it's good to have a package for gathering data from the protocol, serving data to clients, and some common stuff.

P.s. I branched off illia-malachyn/7657-fork-aware-events-streaming-endpoints

This is the commit with all the changes 3d38688 (there's some commits afterwards with small fixes)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 198 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cmd/access/node_builder/access_node_builder.go	0.00%	82 Missing ⚠️
cmd/observer/node_builder/observer_builder.go	0.00%	76 Missing ⚠️
access/mock/api.go	0.00%	34 Missing ⚠️
cmd/util/cmd/run-script/cmd.go	0.00%	4 Missing ⚠️
access/legacy/handler.go	0.00%	2 Missing ⚠️

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[illia-malachyn]

@peterargue does it make sense to do this change? Anyway, we do lots of refactoring currently.

[peterargue]

@peterargue does it make sense to do this change? Anyway, we do lots of refactoring currently.

I agree with refactoring the APIs under a shared module. My preference would be to move it under /access/ instead of /engine/access, then have the engines, simply stand up the servers.

with that said, I would rather we take this on after merging the feature branch back into master. There are more API changes coming to support scheduled transactions, so if we can wait on some restructuring type work like this, it will make maintaining the feature branch easier.