[chore] Return nil from storage factories when there is an error in creating span reader

[mahadzaryab1]

Which problem is this PR solving?

• Towards How to capture storage metrics #6219

Description of the changes

• This PR makes a minor fix to return nil in the cassandra and es storage factories when there is an error creating the storage factory before decorating it

How was this change tested?

• CI

Checklist

• I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
• I have signed all commits
• I have added unit tests for the new functionality
• I have run lint and test steps successfully
  • for jaeger: make lint test
  • for jaeger-ui: yarn lint and yarn test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.24%. Comparing base (57a19af) to head (846db53).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6293      +/-   ##
==========================================
+ Coverage   96.22%   96.24%   +0.01%     
==========================================
  Files         356      356              
  Lines       20432    20432              
==========================================
+ Hits        19661    19665       +4     
+ Misses        583      581       -2     
+ Partials      188      186       -2     

Flag	Coverage Δ
badger_v1	8.90% <0.00%> (ø)
badger_v2	1.62% <0.00%> (ø)
cassandra-4.x-v1-manual	14.84% <0.00%> (ø)
cassandra-4.x-v2-auto	1.56% <0.00%> (ø)
cassandra-4.x-v2-manual	1.56% <0.00%> (ø)
cassandra-5.x-v1-manual	14.84% <0.00%> (ø)
cassandra-5.x-v2-auto	1.56% <0.00%> (ø)
cassandra-5.x-v2-manual	1.56% <0.00%> (ø)
elasticsearch-6.x-v1	18.60% <0.00%> (ø)
elasticsearch-7.x-v1	18.68% <0.00%> (+<0.01%)	⬆️
elasticsearch-8.x-v1	18.84% <0.00%> (+<0.01%)	⬆️
elasticsearch-8.x-v2	1.61% <0.00%> (ø)
grpc_v1	10.37% <0.00%> (ø)
grpc_v2	7.86% <0.00%> (-0.01%)	⬇️
kafka-v1	8.58% <0.00%> (ø)
kafka-v2	1.62% <0.00%> (ø)
memory_v2	1.62% <0.00%> (ø)
opensearch-1.x-v1	18.73% <0.00%> (+<0.01%)	⬆️
opensearch-2.x-v1	18.72% <0.00%> (ø)
opensearch-2.x-v2	1.61% <0.00%> (ø)
tailsampling-processor	0.45% <0.00%> (ø)
unittests	95.15% <100.00%> (+0.01%)	⬆️

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