chore(docs): add an Error handling sample

[vishald123]

Fixes #83 (it's a good idea to open an issue first for discussion)

• Tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

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[vishald123]

Pull request for the following issue:
#83

[codecov]

Codecov Report

Merging #466 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #466   +/-   ##
=======================================
  Coverage   97.97%   97.97%           
=======================================
  Files           6        6           
  Lines         691      691           
  Branches      161      161           
=======================================
  Hits          677      677           
  Misses          2        2           
  Partials       12       12

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[googlebot]

CLAs look good, thanks!

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[stephenplusplus]

Looks good. So, did we delete this sample file at some point, and now we're bringing it back?

[AVaksman]

Looks good. So, did we delete this sample file at some point, and now we're bringing it back?

It was deleted some time ago #110.
And now it looks like there is a request to add it back (link)

[stephenplusplus]

How can we make sure this new sample will have a home on the docs site and not be axed again?

[AVaksman]

Perhaps bring it up on the chat and ask Frank Natividad?

[stephenplusplus]

cc @frankyn!

[frankyn]

Summoning my colleague @BenWhitehead, who is my point person for Datastore/Firestore related DevEx.

[BenWhitehead]

I'll poke around in docsite and figure out how/where this was published before and circle back.

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[AVaksman]

@googlebot I consent.

[googlebot]

CLAs look good, thanks!

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[bcoe]

this is awesome, another sample is always appreciated.

[bcoe]

we tend to use an async function called main these days, here's a sample from the guidelines document:

function main(arg1 = 'default_value_one', arg2 = 1234) {
  // [START your_region_tag]
  /**
   * TODO(developer): Uncomment these variables before running the sample.
   */
  // const arg1 = 'default_value_one';
  // const arg2 = 1234;

  // Imports the Google Cloud Some API library
  const {SomeApiClient} = require('@google-cloud/some-api');

  // Instantiates a client
  const someApiClient = new SomeApiClient();

  async function doSomething() {
    ...
  }

  doSomething();
  // [END your_region_tag]
}

main(...process.argv.slice(2));