draft: attempt to unify process-compose settings

[sandydoo]

I started updating process.process-compose to allow overriding individual settings without losing any of the defaults. But I noticed that, despite the description, those settings are never used.

What needs to be fixed

Name	Type	Default	Comment
process.process-compose	attrs	{ version = "0.5"; ... }	Claims to control top-level settings. Only used for tui and unix-socket.
process.process-compose.tui	any	true	Controls the --tui CLI option
process.process-compose.unix-socket	any	"${config.devenv.runtime}/pc.sock"	Sets the --unix-socket path.
process.process-compose.settings	yaml	{} implementation in config	Claims to modify process-specific settings. Controls top-level settings in reality.
process-managers.process-compose.settings.tui	bool	lib.mkDefault true	Never used. Not a PC setting AFAIKT, only command-line.
process-managers.process-compose.settings.port	int	lib.mkDefault 9999	Never used. Not a PC settings AFAIKT, only command-line.

Other issues

• tui = false; breaks process-compose. Fixed by serializing the bool to true or false, instead of "1" and "".
• PC_TUI_ENABLED doesn't exist in process-compose. There's PC_DISABLE_TUI though. edit: nevermind, looks like this exists for backwards-compatibility with previous devenv versions. We should document this. See https://github.com/cachix/devenv/issues/1109.

Proposal

Name	Action
process.process-compose	Deprecate. If this was previously used for settings, migrate to process-managers.process-compose.settings.
process.process-compose.tui	Move to process-managers.process-compose.tui.
process.process-compose.unix-socket	Move to process-managers.process-compose.unixSocket. Or unix-socket 🤷.
process-managers.process-compose.settings	Fix description to say that this controls the top-level options
process-managers.process-compose.settings.port	Move to process-managers.process-compose.port.
process-managers.process-compose.settings.tui	Remove. Migrate if previously used.
process-managers.process-compose.useUnixSocket	Add. Set to true by default and controls the --use-uds CLI flag. Or enable when port = 0.

[sandydoo]

Relevant example: https://github.com/cachix/devenv/issues/1104#issuecomment-2068232549

[domenkozar]

We also should update examples and docs and make sure all options are deprecated/renamed.