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/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.
+"""]]