Add java queue size term

[ryanholmberg291]

Description

Added a new entry for the Java size() method under queue methods.
The entry explains what size() does, provides syntax, and includes an example.
This contributes to the existing queue concept documentation.

Issue Solved

Closes #7368

Type of Change

• Adding a new entry
• Editing an existing entry (fixing a typo, bug, issues, etc)
• Updating the documentation

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issue Solved section.

[CLAassistant]

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[mamtawardhani]

Hey @ryanholmberg291, please:

• Sign the CLA
• Remove the other files from this branch and only keep the content/java/concepts/queue/terms/size/size.md file on this branch.

Let me know when these things are done, thank you!