rpc: Switch hyper-proxy to use rustls

[mzabaluev]

Fixes: informalsystems/hermes#1641

The rest of the stack already uses rustls for their TLS needs.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1068 (1702069) into master (a121189) will increase coverage by 0.3%.
The diff coverage is n/a.

❗ Current head 1702069 differs from pull request most recent head 40d5302. Consider uploading reports for the commit 40d5302 to get more accurate results

@@           Coverage Diff            @@
##           master   #1068     +/-   ##
========================================
+ Coverage    62.7%   63.1%   +0.3%     
========================================
  Files         236     236             
  Lines       21192   21058    -134     
========================================
- Hits        13296   13292      -4     
+ Misses       7896    7766    -130     

Impacted Files	Coverage Δ
abci/src/codec.rs	87.8% <0.0%> (-1.4%)	⬇️
testgen/src/vote.rs	84.0% <0.0%> (-0.9%)	⬇️
abci/src/server.rs	8.8% <0.0%> (-0.4%)	⬇️
tendermint/src/node.rs	63.5% <0.0%> (-0.2%)	⬇️
testgen/src/header.rs	79.3% <0.0%> (+0.6%)	⬆️
tendermint/src/hash.rs	65.1% <0.0%> (+33.1%)	⬆️

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