Remove io/ioutil package due to deprecation

[Kourin1996]

Description

Replace all functions in io/ioutil package to corresponding functions in os package because io/ioutil package has been marked as decrecated from Go1.16 according to Official Release Notes https://go.dev/doc/go1.16#ioutil.

There won't be any change after replacing these functions to the new functions this doc is mentioning because most of the latest implementations in io/ioutil package are just wrappers of the functions in os.

Implementation of io/ioutil at Go 1.17: https://cs.opensource.google/go/go/+/refs/tags/go1.17:src/io/ioutil/ioutil.go

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

Please complete this section if you ran manual tests for this functionality, otherwise delete it

Documentation update

Please link the documentation update PR in this section if it's present, otherwise delete it

Additional comments

Please post additional comments in this section if you have them, otherwise delete it

[codecov]

Codecov Report

Merging #723 (ae6ee05) into develop (c39d854) will decrease coverage by 0.02%.
The diff coverage is 41.66%.

@@             Coverage Diff             @@
##           develop     #723      +/-   ##
===========================================
- Coverage    52.51%   52.48%   -0.03%     
===========================================
  Files          130      130              
  Lines        17069    17069              
===========================================
- Hits          8964     8959       -5     
- Misses        7462     7466       +4     
- Partials       643      644       +1     

Impacted Files	Coverage Δ
chain/chain.go	28.69% <0.00%> (ø)
chain/chain_bindata.go	32.31% <0.00%> (ø)
jsonrpc/jsonrpc.go	18.23% <0.00%> (ø)
secrets/config.go	0.00% <0.00%> (ø)
consensus/ibft/fork/helper.go	81.81% <50.00%> (ø)
secrets/local/local.go	75.70% <50.00%> (ø)
network/e2e_testing.go	63.89% <100.00%> (ø)
state/runtime/precompiled/testing.go	80.43% <100.00%> (ø)
tests/testing.go	69.33% <100.00%> (ø)
network/server_discovery.go	73.88% <0.00%> (-1.92%)	⬇️
... and 1 more

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[zivkovicmilos]

Looks good 💯