Add conditional validation for urls

[ericnewcomer]

Fixes: #772

[codecov]

Codecov Report

Merging #773 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #773      +/-   ##
==========================================
+ Coverage   64.12%   64.17%   +0.05%     
==========================================
  Files         164      164              
  Lines        6087     6091       +4     
  Branches     1417     1418       +1     
==========================================
+ Hits         3903     3909       +6     
+ Misses       1751     1750       -1     
+ Partials      433      432       -1

Impacted Files	Coverage Δ
...ponents/flow/routers/webhook/WebhookRouterForm.tsx	88.57% <100%> (ø)	⬆️
src/store/validators.ts	68.04% <100%> (+1.37%)	⬆️
src/components/flow/routers/webhook/helpers.ts	67.64% <0%> (+2.94%)	⬆️
src/components/simulator/helpers.ts	47.61% <0%> (+4.76%)	⬆️

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[nicpottier]

So basically this is only doing URL validation in the cases where there are no expressions is that right?

[rowanseymour]

Looks good - just need nyaruka/goflow#815 as well so that we handle invalid URLs gracefully in the engine