add an "import" `[-i FILEPATH]` to `airflow connections` cli command

[andres-lowrie]

Description

This would allow users to create a bunch of connections at once from a file.

Use case / motivation

I think having some parody between the connections and variables commands could be beneficial and provide a more pleasant UX for cli users.

For example when I did airflow connections -h and didn't see a -i it felt weird seeing as how this is possible for variables.

So I was left feeling a little confused; I was expecting it to be there

[boring-cyborg]

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[mik-laj]

Duplicate: #9855