[Concept Entry] Postgresql transactions

[codecademy-docs]

Reason/inspiration (optional)

We would like a new entry on the Transactions concept under PostgreSQL. The entry should go in a new file under docs/content/postgresql/concepts/transactions/transactions.md.

The entry should include:

• An introductory paragraph that describes the concept
• A ‘Syntax’ section that includes the syntax for the concept (if applicable)
• An ‘Example’ section that shows the concept in use

Please refer to the concept entry template, content standards, and markdown style guide when working on the PR for this issue.

Entry Type (select all that apply)

New Concept Entrty for Existing Topic

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