Spike: DID resolver

[shannonwells]

Goal

The goal of this PR is to make a Frequency-DSNP-DID resolver RPC endpoint.

Closes #685
Partially blocked by #474 fetching keys for a given MSA ID

Discussion

Creates a couple of RPC endpoints, one of which returns a DID document for an ID if it's an MSA. The others are TBD

Checklist

• Updated js/api-augment.
• Tests added

[codecov]

Codecov Report

Merging #724 (61a75a6) into main (ec9ab3a) will increase coverage by 0.77%.
The diff coverage is 85.48%.

❗ Current head 61a75a6 differs from pull request most recent head 8e7f6e8. Consider uploading reports for the commit 8e7f6e8 to get more accurate results

@@            Coverage Diff             @@
##             main     #724      +/-   ##
==========================================
+ Coverage   79.58%   80.36%   +0.77%     
==========================================
  Files          19       20       +1     
  Lines         823      886      +63     
==========================================
+ Hits          655      712      +57     
- Misses        168      174       +6     

Impacted Files	Coverage Δ
pallets/msa/src/rpc/src/lib.rs	51.72% <80.00%> (+51.72%)	⬆️
pallets/msa/src/lib.rs	84.68% <87.50%> (+0.46%)	⬆️
common/primitives/src/did.rs	94.73% <94.73%> (ø)
pallets/messages/src/lib.rs	86.17% <0.00%> (-0.65%)	⬇️

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[wilwade]

Closing out the spike, but retaining branch.