docs(samples): added quickstart sample

[galdawave]

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Fixes #<issue_number_goes_here> 🦕

[conventional-commit-lint-gcf]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

-- conventional-commit-lint bot
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[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/snippets/quickstart_sample.py:17, tag documentai_quickstart

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