docs(samples): add list configs

[stephaniewang526]

No description provided.

[google-cla]

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[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.

[codecov]

Codecov Report

Merging #306 into master will decrease coverage by 9.37%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #306      +/-   ##
============================================
- Coverage     74.68%   65.31%   -9.38%     
+ Complexity      108       93      -15     
============================================
  Files             7        7              
  Lines           948      591     -357     
  Branches         18        5      -13     
============================================
- Hits            708      386     -322     
+ Misses          220      188      -32     
+ Partials         20       17       -3     

Impacted Files	Coverage Δ	Complexity Δ
...nsfer/v1/stub/DataTransferServiceStubSettings.java	75.95% <0.00%> (-5.60%)	23.00% <0.00%> (-1.00%)
...atransfer/v1/stub/GrpcDataTransferServiceStub.java	92.02% <0.00%> (-4.13%)	20.00% <0.00%> (-1.00%)
...ery/datatransfer/v1/DataTransferServiceClient.java	61.93% <0.00%> (+0.04%)	44.00% <0.00%> (-13.00%)	⬆️
...y/datatransfer/v1/DataTransferServiceSettings.java	12.96% <0.00%> (+0.23%)	2.00% <0.00%> (ø%)

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[pmakani]

Fixed #308