Specification of the connection file

Problem

The connection file is documented aside the kernel protocol documentation, but it is not specified.

Proposed Enhancement

We propose to specify the connection file with the JSON schema joined in this PR. The specification would reflect the current description of the connection file.

The documentation of the connection file will be stored along side those of the kernel protocol while its specification will be stored in the Jupyter schema repo.

Impact on existing implementations

None, this JEP only specifies the current implementations.