add e2e test with known signed-blinded-beacon-block

[metachris]

📝 Summary

Use known SignedBlindedBeaconBlock for e2e test

---

✅ I have run these commands

• make lint
• make test-race
• go mod tidy

[codecov-commenter]

Codecov Report

Merging #326 (f47448e) into main (97207c6) will increase coverage by 0.60%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #326      +/-   ##
==========================================
+ Coverage   82.14%   82.75%   +0.60%     
==========================================
  Files           5        5              
  Lines         661      661              
==========================================
+ Hits          543      547       +4     
+ Misses         90       87       -3     
+ Partials       28       27       -1     

Flag	Coverage Δ
unittests	82.75% <ø> (+0.60%)	⬆️

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

Impacted Files	Coverage Δ
server/service.go	81.72% <0.00%> (+1.01%)	⬆️

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