add slither analysis github action

[artdgn]

## This PR is blocked until crytic/slither#919 is resolved (slither doesn't still support custom errors). No longer blocked after https://github.com/crytic/slither/releases/tag/0.8.2

Tasks:

• Ensure slither-local command in synthetix-main works (should print analysis results in terminal).
• Ensure slither-sarif command in synthetix-main works (should create a sarif format file).
• Ensure the sarif file is picked up in PRs and pushes and the analysis is shown in PRs diffs and "checks" tabs.
• Add slither analysis for core-contracts & core-modules and not only synthetix-main sub packages.
• Look into the released github-action https://github.com/marketplace/actions/slither-action

[codecov]

Codecov Report

Merging #484 (cbfad1b) into main (5f6b998) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #484   +/-   ##
=======================================
  Coverage   97.16%   97.16%           
=======================================
  Files          71       71           
  Lines        1233     1233           
  Branches       62       62           
=======================================
  Hits         1198     1198           
  Misses         35       35           

Flag	Coverage Δ
core-contracts	100.00% <ø> (ø)
core-js	99.25% <ø> (ø)
core-modules	100.00% <ø> (ø)
deployer	96.34% <ø> (ø)
synthetix-main	100.00% <ø> (ø)

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[artdgn]

Updated the PR with latest main.

It seems that slither is having difficulties:

• when running in core-contracts it errors out with an error similar to Custom error imported from library is converted to high level call crytic/slither#1001 and Function not found during IR conversion crytic/slither#776. Probably related to IR conversion of a library method.
• when run in synthetix-main it can't find the contracts imported from core-contracts for some reason.

I guess worth to wait for resolutions of the errors on slither side.

[dbeal-eth]

I believe we have decided we don't want slither.