[tfswitch-parity] Transparently support .tfswitchrc files.

[kvendingoldo]

Describe the solution you'd like
Please replicate this feature from tfswitch. https://tfswitch.warrensbox.com/Quick-Start/#use-tfswitchrc-file

Additional context
It's backport of the original issue from tofuenv: tofuutils/tofuenv#35
cc @skyzyx

[dvaumoron]

Priority between .tfswitchrc and .terraform-version files ? Do we need to support something like .tofuswitchrc for the OpenTofu part ?

[dvaumoron]

Changed to check .tfswitchrc in working directory after .terraform-version there, and before user home directory or root directory (no search of .tfswitchrc in those other places).

No modification on the OpenTofu management part.