Clarify error message when connector ID must be disambiguated

[djaglowski]

Resolves #8120

[djaglowski]

This is technically user facing but in my opinion is minor enough that it does not warrant a changelog. Happy to add one if maintainers disagree.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.06 🎉

Comparison is base (a1efc0e) 90.18% compared to head (bfcdf82) 90.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8121      +/-   ##
==========================================
+ Coverage   90.18%   90.24%   +0.06%     
==========================================
  Files         301      301              
  Lines       15377    15453      +76     
==========================================
+ Hits        13868    13946      +78     
+ Misses       1222     1221       -1     
+ Partials      287      286       -1     

Impacted Files	Coverage Δ
otelcol/config.go	100.00% <100.00%> (ø)
service/internal/proctelemetry/config.go	96.75% <100.00%> (+2.06%)	⬆️
service/telemetry/config.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[mx-psi]

Thanks! Agreed that no changelog is needed