fix: Update Azure Functions Detector to Only Detect When Function Version is Defined

[JacksonWeber]

Which problem is this PR solving?

Azure Functions Detector should only detect Azure Functions when the function version is set. Currently it is erroneously detecting functions when in app service.

[trentm]

Notes to self:

Currently it is erroneously detecting functions when in app service.

"Azure App Service" is a base service for a number of Azure services, of which Azure Functions is one. So the presence of the WEBSITE_SITE_NAME envvar is not sufficient to identify this as being an Azure Function.

Docs on envvars in App Service here: https://learn.microsoft.com/en-us/azure/app-service/reference-app-settings
And the subset of envvars in Azure Functions here: https://learn.microsoft.com/en-us/azure/app-service/reference-app-settings?tabs=kudu%2Cdotnet#functions

[hectorhdzg]

LGTM

[codecov]

Codecov Report

Merging #1846 (d30c964) into main (094fd6f) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1846   +/-   ##
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  Coverage   91.49%   91.49%           
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  Files         144      144           
  Lines        7388     7388           
  Branches     1474     1474           
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  Hits         6760     6760           
  Misses        628      628           

Files	Coverage Δ
...ctor-azure/src/detectors/AzureFunctionsDetector.ts	100.00% <100.00%> (ø)