docs(samples): add quickstart sample

[stephaniewang526]

Fixes b/176624168

[snippet-bot]

Here is the summary of changes.

You added 1 region tag.

• samples/snippets/src/main/java/com/example/bigqueryreservation/QuickstartSample.java:19, tag bigqueryreservation_quickstart

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[codecov]

Codecov Report

Merging #302 (f8c0226) into master (8ec3351) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #302 +/- ## ========================================= Coverage 82.96% 82.96% Complexity 171 171 ========================================= Files 6 6 Lines 1168 1168 Branches 22 22 ========================================= Hits 969 969 Misses 172 172 Partials 27 27 

---

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 8ec3351...f8c0226. Read the comment docs.