readme: Add two greeter implementations

chore: set dir to absolute path

Derive VtSelection::default

Use strip_prefix to strip prefix

No need to do it manually.

Remove pointless copying of string before copying it

Remove references that are implicitly dereferenced

This are implicitly dereferenced by the compiler and a no-op.

Remove no-op question mark and Ok()

cargo update

Drop unmaintained `users` crate

Its functionality is provided by the `nix` crate which is already a
dependency anyway.

See: https://rustsec.org/advisories/RUSTSEC-2023-0040.html

Update deprecated SPDX identifier for GPL-3.0-only

Link the LICENSE file into the greetd_ipc crate to ensure that it
appears in the crates.io archive.

Minimize user-exposed environment variables

PAM requires a number of environment variables set, and greeters need to
know the greetd socket path. All these environment variables were set
for all sessions started by greetd.

Only set the greetd socket path for greeter sessions, and remove some
environment variables only need for PAM before starting a session.

server: cargo fmt

config: Fix tests for service config

agreety: Return error if no input when prompted

If EOF is provided when the user is prompted agreety would panic. This
commit fixes that by returning an error instead causing graceful exit(1)
instead.

config: allow using custom PAM configs

In the event several greeters are installed, each needing a specific PAM
config, it could be useful to have each greeter having its own config
file (which is already possible), each one indicating the PAM config to
be used with this greeter (which is not possible for now).

This commit adds a new (optional) "service" key to the "general",
"default_session" and "initial_session" sections so users and/or
distributions can have more flexibility regarding PAM config management.

In case this option is missing from the config file, we fall back to the
default "greetd" and "greetd-greeter" config names.

Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>

Add ReGreet to list of known greetd greeters

Bump version to 0.9.0

cargo: Update dependencies

readme: Add ddlm, note list updates welcome

cargo: Update tokio