pre-init config and hook

Added annex.pre-init-command git config and pre-init-annex hook that is run
before git-annex repository initialization.

This can block initialization. Or it can preform pre-initialization
configuration or tweaking.

I left stdio connected while it's running, so it could also be used for
interactive prompting conceivably, although that would want to use /dev/tty
anyway probably in order to not pollute the stdout of a command when
automatic initialization is done.

Sponsored-by: Dartmouth College's OpenNeuro project

doc/git-annex-init.mdwn

@@ -27,7 +27,11 @@ already initialized git-annex repository.
 A top-level `.noannex` file will prevent git-annex init from being used
 in a repository. This is useful for repositories that have a policy
 reason not to use git-annex. The content of the file will be displayed
-to the user who tries to run git-annex init.
+to the user who tries to run git-annex init. 
+
+The annex.pre-init-command git configuration or pre-init-annex hook
+is run before initialization and can exit nonzero as well to prevent
+initialization, as well as doing other setup.
 
 # EXAMPLES
 

doc/git-annex.mdwn

@@ -1176,6 +1176,16 @@ repository, using [[git-annex-config]]. See its man page for a list.)
   Alternatively, a hook script can be installed in
   `.git/hooks/pre-commit-annex`
 
+* `annex.pre-init-command`
+
+  This command is run before the repository is initialized, either by
+  `git-annex init`, or automatic initialization. It can configure
+  the repository in any way needed. If it exits nonzero, the repository
+  initialization will fail.
+  
+  Alternatively, a hook script can be installed in
+  `.git/hooks/pre-init-annex`
+
 * `annex.alwayscompact`
 
   By default, git-annex compacts data it records in the git-annex branch.

doc/todo/Support___40__globally_configured__41_____34__annex_init__34___hooks.mdwn

@@ -6,3 +6,5 @@ The idea is stemmed from discussions/problems with using freeze/thaw hooks, and
 
 [[!meta author=yoh]]
 [[!tag projects/openneuro]]
+
+> [[done]] --[[Joey]]

doc/todo/Support___40__globally_configured__41_____34__annex_init__34___hooks/comment_5_c1687c1d853159debff18ed5c75268ad._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 5"""
+ date="2025-01-13T17:33:02Z"
+ content="""
+Note that the `.noannex` file that prevents init has some overlap with
+a pre-init hook that exits nonzero. I guess the .noannex file has the
+benefit of working in every clone of a repository without additional
+configuration.
+"""]]

doc/todo/Support___40__globally_configured__41_____34__annex_init__34___hooks/comment_6_e2e93b900f018d276029389405a09c28._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 6"""
+ date="2025-01-13T18:17:42Z"
+ content="""
+Implemented .git/hooks/pre-init-annex 
+(and alternatively git config annex.pre-init-command)
+
+Note that this is also run before automatic initialization.
+"""]]