[Term Entry] Swift dictionaries keys()

[codecademy-docs]

Reason/inspiration (optional)

"We would like a new term entry on the keys for Dictionaries in Swift. The entry should go in a new file under content/swift/concepts/dictionaries/terms/keys/keys.md The entry should include the following:

• A description of the term
• A ##Syntax section that includes the syntax of the method and its details
• An ##Example section that includes a swift codeblock and shell that shows the example

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

Entry Type (select all that apply)

New Term for Existing Concept Entry

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