🚶 Offline flow tweaks

[rowanseymour]

• Change send_msg to always send a message even if it can't resolve channel/URN
• Validate flow types

[codecov]

Codecov Report

Merging #425 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #425      +/-   ##
==========================================
+ Coverage   66.76%   66.78%   +0.02%     
==========================================
  Files         157      157              
  Lines        8277     8282       +5     
==========================================
+ Hits         5526     5531       +5     
  Misses       2382     2382              
  Partials      369      369

Impacted Files	Coverage Δ
cmd/flowrunner/main.go	46.59% <ø> (ø)	⬆️
flows/msg.go	18.51% <ø> (ø)	⬆️
flows/actions/send_msg.go	100% <100%> (ø)	⬆️
flows/definition/flow.go	70.58% <100%> (+0.58%)	⬆️

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