feat(bigtable): pass default app profile ID in quickstart

[elinorli]

Update the quickstart example to explicitly configure the Table instance with the "default" application profile ID using AppProfileIdOption.

[gemini-code-assist]

Code Review

This pull request updates the cbt::Table initialization in both the README and the quickstart example to explicitly include a default App Profile ID using google::cloud::Options. I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.70%. Comparing base (3852865) to head (fd1e079).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16091      +/-   ##
==========================================
- Coverage   92.70%   92.70%   -0.01%     
==========================================
  Files        2353     2353              
  Lines      218352   218352              
==========================================
- Hits       202425   202421       -4     
- Misses      15927    15931       +4     

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