add wstETH price aggregator

[thorseldon]

• Custom price aggregator for wstETH/ETH;
• Calculate the wstETH price from Chainlink's stETH/ETH;
• wstETH Price = stETH Price / tokenPerStETH;

[codecov]

Codecov Report

Attention: Patch coverage is 75.60976% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 90.97%. Comparing base (3bb61af) to head (e28fb09).
Report is 1 commits behind head on main.

❗ Current head e28fb09 differs from pull request most recent head 7f742ee. Consider uploading reports for the commit 7f742ee to get more accurate results

Files	Patch %	Lines
contracts/misc/WstETHPriceAggregator.sol	75.60%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
- Coverage   91.20%   90.97%   -0.23%     
==========================================
  Files          36       37       +1     
  Lines        2819     2860      +41     
  Branches      447      449       +2     
==========================================
+ Hits         2571     2602      +31     
- Misses        248      258      +10     

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