Set splunk.distro.version attr in resource

[MrAlias]

As per the GDI specification: https://github.com/signalfx/gdi-specification/blob/main/specification/semantic_conventions.md#splunk-resource-attributes

[pellared]

Consider adding a line in the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #332 (c56744e) into main (b3e4c19) will decrease coverage by 0.04%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #332      +/-   ##
==========================================
- Coverage   79.14%   79.10%   -0.05%     
==========================================
  Files          54       54              
  Lines        2700     2709       +9     
==========================================
+ Hits         2137     2143       +6     
- Misses        521      523       +2     
- Partials       42       43       +1     

Flag	Coverage Δ
Linux	79.10% <66.66%> (-0.05%)	⬇️
macOS	?

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Impacted Files	Coverage Δ
distro/otel.go	66.66% <66.66%> (ø)

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