tmuxinator/962: add named window/pane support

[iznoel]

This is a contribution to tmuxinator, cc @hschne, following issue 962

In essence, Current schema does not recognize named windows / panes, only anonymous ones
This branch attempts to

• generalizing the Window and Pane objects
• introduce their discovery with named objects
  {windows: [{$wname: <window>{panes: [{$pname: <pane>}, ...]}}, ...]}
• versus the current schema that's using
  { windows: [ <window>{panes: <pane>{}}] }

Current tmuxinator testsuite already uses this configuration variant
But this setup should allow for completion to work correctly aswell

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @madskristensen and @hyperupcall - if they write a comment saying "LGTM" then it will be merged.

[iznoel]

so src/test/tmuxinator/sample.deprecations.yml fails, a config like doesn't appear valid for tmuxinator v3.3.5 anyhow 🤷

[hyperupcall]

Feel free to remove anything that's invalid if you're absolutely sure, once CI goes green I can merge!