Refactor conf with flatten

[nitely]

Changes:

• Pack metric opts into MetricsConf
• Pack keymanager opts into keyManagerApiConf
• Pack restRequestTimeout, restMaxRequestBodySize, restMaxRequestHeadersSize into RestApiConf. But this could be passed individually instead.
• Small initKeymanagerServer change to avoid passing rest opts.
• Clean up no longer needed defaultValueDesc
• Bumped nim-confutils to Fixes #114; Allow flattening options in objects nim-confutils#118

Beware this contains breaking changes; needs status-im/nimbus-eth1#3848 to be merged after to solve them.

[github-actions]

Unit Test Results

       12 files  ±0    2 816 suites  ±0   1h 10m 15s ⏱️ - 9m 40s
15 853 tests ±0  14 288 ✔️ ±0  1 565 💤 ±0  0 ❌ ±0 
76 516 runs  ±0  74 776 ✔️ ±0  1 740 💤 ±0  0 ❌ ±0 

Results for commit 810ee2a. ± Comparison against base commit 2f5f186.

♻️ This comment has been updated with latest results.

[cheatfate]

If you going to refactor configs it would be nice if you split all the configs between parts, because when VC builds it imports whole BN codebase just because of the conf.nim. So it would be nice to have some module with common procedures (which does not import whole BN) and separate conf.nim for every binary we have.

[arnetheduck]

nice if you split all the configs between parts

It's not a bad idea in general but I suspect the gains might be smaller than one would think since the VC already needs a significant portion of spec which is the main part of what's being imported "redundantly". One would also need to introduce additional structure for parsing those options that are common, so it's probably outside of the scope of this PR.

[tersec]

nim-confutils bump done externally to this PR.