Add docs for show external connection

[katmayb]

Fixes DOC-10317

This PR adds the SHOW EXTERNAL CONNECTION statement to the docs.

[github-actions[bot]]

Files changed:

• src/current/_includes/v24.2/sidebar-data/sql.json
• src/current/v24.2/create-external-connection.md
• src/current/v24.2/drop-external-connection.md
• src/current/v24.2/set-up-physical-cluster-replication.md
• src/current/v24.2/show-create-external-connection.md
• src/current/v24.2/show-external-connection.md

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[katmayb]

@rharding6373 do you mind reviewing this one?