refactor: rename project from remind_sync to ical2rem

- Rename executable public_name and package name from remind_sync to
  ical2rem
- Update dune-project with new name, source URI, maintainer, synopsis,
  description, and tags
- Add dune-build-info dependency and use Build_info to generate the
  version string at build time instead of the %%VERSION%% placeholder
- Add pinned dependencies to ical2rem.opam
- Remove remind_sync.opam
- Bump dune lang version from 3.20 to 3.23

bin/dune

@@ -1,10 +1,11 @@
 (executable
- (public_name remind_sync)
+ (public_name ical2rem)
  (name main)
  (modules main commandLine remind eventPredicates utils windows_tz)
  (preprocess
   (pps ppx_deriving.show))
  (libraries
+  dune-build-info
   cmdliner
   icalendar
   timedesc-tzdb.full