feat: added samples for api-endpoints

[bradmiro]

Adding code for api-endpoints sample. Style is to match Python canonical: https://github.com/GoogleCloudPlatform/python-docs-samples/blob/750d2f6d36b1a030f7226067922c8ac3dab3a39b/automl/beta/set_endpoint.py

[codecov]

Codecov Report

Merging #259 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #259   +/-   ##
=======================================
  Coverage   71.42%   71.42%           
=======================================
  Files           2        2           
  Lines           7        7           
=======================================
  Hits            5        5           
  Misses          2        2

---

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 0c5cd22...e69d442. Read the comment docs.

[bradmiro]

Samples test fail -> The test that's failing (the new one) passed locally. The dataset is in our client libraries project

Docs fail -> there's a broken link that points to a file that is included with this PR. Should be fixed after merging.

[bcoe]

@bradmiro by default the project we use for Node.js tests is long-door-651, is there a chance it needs to have this feature enabled?

[bradmiro]

@bcoe I used a service account created in long-door-651 for testing. Hmm...

Edit: fixed :)