Add shared state async node

[javierbrk]

This is a proposal to implement an improvement on current shared state base infrastructure.

[codecov-commenter]

Codecov Report

Merging #1030 (68ec849) into master (4cce5b5) will increase coverage by 1.44%.
The diff coverage is 70.32%.

❗ Current head 68ec849 differs from pull request most recent head 6f0b191. Consider uploading reports for the commit 6f0b191 to get more accurate results

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@@            Coverage Diff             @@
##           master    #1030      +/-   ##
==========================================
+ Coverage   77.84%   79.28%   +1.44%     
==========================================
  Files          52       53       +1     
  Lines        4388     4447      +59     
==========================================
+ Hits         3416     3526     +110     
+ Misses        972      921      -51     

Files Changed	Coverage Δ
...-lime-utils/files/usr/lib/lua/lime-utils-admin.lua	57.14% <2.77%> (-35.59%)	⬇️
...es/lime-system/files/usr/lib/lua/lime/firewall.lua	64.00% <14.28%> (+19.26%)	⬆️
...us-lime-metrics/files/usr/lib/lua/lime-metrics.lua	86.36% <36.36%> (-6.23%)	⬇️
...kages/lime-system/files/usr/lib/lua/lime/utils.lua	85.22% <71.42%> (-0.58%)	⬇️
...e-proto-bmx7/files/usr/lib/lua/lime/proto/bmx7.lua	71.08% <78.57%> (+5.79%)	⬆️
...ges/lime-system/files/usr/lib/lua/lime/network.lua	78.39% <80.48%> (+3.05%)	⬆️
...-lime-utils/files/usr/lib/lua/lime/node_status.lua	83.51% <83.51%> (ø)
...wrt-wan/files/usr/lib/lua/lime/hwd/openwrt_wan.lua	100.00% <100.00%> (ø)
...oto-babeld/files/usr/lib/lua/lime/proto/babeld.lua	95.94% <100.00%> (+0.05%)	⬆️
...oto-batadv/files/usr/lib/lua/lime/proto/batadv.lua	96.36% <100.00%> (-0.52%)	⬇️
... and 5 more

... and 1 file with indirect coverage changes

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[G10h4ck]

I think this change would silently break other components using that data like lime app, and anyway is unrelated to the PR, let's keep it out.

[G10h4ck]

This block should be removed as source tree override should be used for that purpose as explained by Jow here https://forum.archive.openwrt.org/viewtopic.php?id=46916