Complete redesign of Subsurface version numbers

- for now all versions start with v6.0
- CICD builds use the monolithic build number as patch level, e.g. v6.0.12345
- local builds use the following algorithm
  - find the newest commit with a CICD build number that is included in the
    working tree
  - count the number of commits in the working tree since that commit
  - if there are no commits since the last CICD build, the local build version
    will be v6.0.12345-local
  - if there are N commits since the last CICD build, it will be
    v6.0.12345-N-local
- test builds in the CICD that don't create artifacts simply use a dummy release
  in order to not incorrectly increment the build number and also not to waste
  time and resources by manually checking out the nightly-build repo for each of
  these builds.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

core/version.c

@@ -1,9 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "ssrf-version.h"
 
+// let's leave the two redundant functions in case we change our minds on git SHAs
 const char *subsurface_git_version(void)
 {
-	return GIT_VERSION_STRING;
+	return CANONICAL_VERSION_STRING_4;
 }
 
 const char *subsurface_canonical_version(void)