Deprecate steampipe-plugins input in favor of plugin-connections input

[cbruno10]

As part of v1.4.0 changes, we are deprecating the steampipe-plugins input in favor of plugin-connections. The new plugin-connections input supports passing in plugin connections as HCL or JSON and follow the same format you'd have in a local .spc or .json file when running Steampipe today.

Current plans are to keep the steampipe-plugins input for backward compatibility with eventual removal in a future major version as a breaking change.

If anyone has any thoughts or inputs, please add them to this issue, thanks!