Add `ConnectorState.Trace` field

[owenthereal]

Kafka Connect's official API doc doesn't have this field but the implementation has it:

• https://github.com/apache/kafka/blob/f0282498e7a312a977acb127557520def338d45c/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/AbstractStatus.java#L46
• https://github.com/apache/kafka/blob/3cdc78e6bb1f83973a14ce1550fe3874f7348b05/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectorStatus.java#L23

This field contains the errors of the connector when there is no task.

[codecov[bot]]

Codecov Report

Merging #10 (f23000f) into master (759c155) will decrease coverage by 1.68%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
- Coverage   87.39%   85.71%   -1.69%     
==========================================
  Files           3        3              
  Lines         119       98      -21     
==========================================
- Hits          104       84      -20     
+ Misses          9        8       -1     
  Partials        6        6              

Impacted Files	Coverage Δ
connectors.go	100.00% <ø> (ø)
client.go	78.68% <0.00%> (-2.75%)	:arrow_down:
errors.go	0.00% <0.00%> (ø)

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[owenthereal]

👋 Does anyone have a chance to review and merge this?