Add connector validation to otelcol

[djaglowski]

Part of #6700

This PR finishes adding connectors to the otelcol config including validation. Validation for connectors is the same as with other components, except two additional checks are included:

1. That each connector is used as an exporter in at least one pipeline, and also as a receiver in at least one pipeline.
2. That each connector ID is distinct from receivers and exporters. (Depends on decision on Add Config method to pipeline component builders #6927 (comment))

[codecov]

Codecov Report

Base: 90.38% // Head: 90.37% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (2db6b73) compared to base (3a0a3c5).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7001      +/-   ##
==========================================
- Coverage   90.38%   90.37%   -0.01%     
==========================================
  Files         243      243              
  Lines       14575    14597      +22     
==========================================
+ Hits        13173    13192      +19     
- Misses       1133     1136       +3     
  Partials      269      269              

Impacted Files	Coverage Δ
otelcol/collector.go	77.44% <100.00%> (+0.17%)	⬆️
otelcol/config.go	96.66% <100.00%> (+1.58%)	⬆️
extension/extension.go	97.61% <0.00%> (-2.39%)	⬇️
exporter/exporter.go	99.00% <0.00%> (-1.00%)	⬇️
receiver/receiver.go	99.00% <0.00%> (-1.00%)	⬇️
processor/processor.go	99.00% <0.00%> (-1.00%)	⬇️
connector/connector.go	99.58% <0.00%> (-0.42%)	⬇️
component/component.go	38.63% <0.00%> (+0.33%)	⬆️

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[jpkrohling]

LGTM, just perhaps one error message could be improved.