docs(samples): add update dataset partition expiration

[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)

[codecov]

Codecov Report

Merging #612 into master will decrease coverage by 1.13%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #612      +/-   ##
============================================
- Coverage     82.63%   81.49%   -1.14%     
- Complexity     1224     1226       +2     
============================================
  Files            77       77              
  Lines          5102     6220    +1118     
  Branches        565      691     +126     
============================================
+ Hits           4216     5069     +853     
- Misses          595      792     +197     
- Partials        291      359      +68     

Impacted Files	Coverage Δ	Complexity Δ
...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	78.48% <0.00%> (-9.12%)	25.00% <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%)
.../java/com/google/cloud/bigquery/FormatOptions.java	44.44% <0.00%> (-3.56%)	12.00% <0.00%> (ø%)
...google/cloud/bigquery/ExternalTableDefinition.java	58.09% <0.00%> (-3.37%)	19.00% <0.00%> (ø%)
... and 47 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 be6a874...87b9214. Read the comment docs.