feat: add labels for writechannelconfiguration

[pmakani]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #343

[codecov]

Codecov Report

Merging #347 into master will decrease coverage by 1.82%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #347      +/-   ##
============================================
- Coverage     79.74%   77.91%   -1.83%     
- Complexity     1184     1188       +4     
============================================
  Files            77       77              
  Lines          5089     6218    +1129     
  Branches        563      690     +127     
============================================
+ Hits           4058     4845     +787     
- Misses          748     1022     +274     
- Partials        283      351      +68     

Impacted Files	Coverage Δ	Complexity Δ
...ogle/cloud/bigquery/WriteChannelConfiguration.java	86.81% <100.00%> (-1.88%)	46.00 <14.00> (+2.00)	⬇️
...com/google/cloud/bigquery/GoogleSheetsOptions.java	77.14% <0.00%> (-12.86%)	10.00% <0.00%> (ø%)
...main/java/com/google/cloud/bigquery/ModelInfo.java	77.21% <0.00%> (-8.92%)	24.00% <0.00%> (ø%)
...in/java/com/google/cloud/bigquery/RoutineInfo.java	67.47% <0.00%> (-7.77%)	21.00% <0.00%> (ø%)
...google/cloud/bigquery/HivePartitioningOptions.java	83.78% <0.00%> (-6.22%)	11.00% <0.00%> (ø%)
...main/java/com/google/cloud/bigquery/DatasetId.java	81.25% <0.00%> (-5.42%)	13.00% <0.00%> (ø%)
.../com/google/cloud/bigquery/ConnectionProperty.java	91.89% <0.00%> (-5.26%)	12.00% <0.00%> (ø%)
.../google/cloud/bigquery/DatastoreBackupOptions.java	88.23% <0.00%> (-5.10%)	8.00% <0.00%> (ø%)
...va/com/google/cloud/bigquery/InsertAllRequest.java	86.25% <0.00%> (-3.75%)	23.00% <0.00%> (ø%)
...in/java/com/google/cloud/bigquery/TableResult.java	85.29% <0.00%> (-3.60%)	15.00% <0.00%> (ø%)
... and 48 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ec2382d...18f3a7e. Read the comment docs.