add RPC backup

[Coiling-Dragon]

Detailed description:

Which issue(s) this PR fixes: Fixes #896

Special notes for your reviewer:

Checklist

• [ ] Documentation added
• [x] Tests updated

[codecov[bot]]

Codecov Report

Merging #899 (dfd2bd5) into main (9101ccb) will increase coverage by 0.28%. The diff coverage is 68.51%.

@@            Coverage Diff             @@
##             main     #899      +/-   ##
==========================================
+ Coverage   63.76%   64.05%   +0.28%     
==========================================
  Files          85       86       +1     
  Lines        6483     6696     +213     
==========================================
+ Hits         4134     4289     +155     
- Misses       2151     2195      +44     
- Partials      198      212      +14     

Flag	Coverage Δ
unittests	64.05% <68.51%> (+0.28%)	:arrow_up:

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

Impacted Files	Coverage Δ
app/clients/evm/client_pool.go	68.07% <68.07%> (ø)
config/node.go	71.96% <100.00%> (ø)

... and 1 file with indirect coverage changes