Add support for MaxOpenConnections

[facs95]

Closes: #XXX

Description

Added support for setting max-open-connections on RPC server listener. Added a new flag json-rpc.max-open-connections.

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #1229 (fd4ac3b) into main (b3242ea) will decrease coverage by 0.00%.
The diff coverage is 6.66%.

@@            Coverage Diff             @@
##             main    #1229      +/-   ##
==========================================
- Coverage   51.92%   51.92%   -0.01%     
==========================================
  Files         102      102              
  Lines        9282     9284       +2     
==========================================
+ Hits         4820     4821       +1     
- Misses       4214     4215       +1     
  Partials      248      248              

Impacted Files	Coverage Δ
server/config/config.go	22.15% <6.66%> (+0.33%)	⬆️