Integrate `eshell' with atuin <https://github.com/atuinsh/atuin>

atuin stores shell history in a database, which allows for having
same history across multiple shells, sessions, and optionally
across different machines.  This package provides functionality to
store and browse eshell history in atuin.

`eshell-atuin-mode' and `eshell-atuin-history' are the
corresponding entrypoints.

See also the package README at
<https://github.com/SqrtMinusOne/eshell-atuin>