Add the experimental git survey command to analyze (large) local repositories (#667)

This command is inspired by [`git
sizer`](https://github.com/github/git-sizer), having the advantage of
being much closer to the internals of Git.

The intention is to provide a built-in command that can be used to
analyze large repositories for performance and scaling problems, for
growth over time, and to correlate with other measurements (in
particular with Trace2 data collected e.g. via
https://github.com/git-ecosystem/trace2receiver/).

Author: dscho

Documentation/config/survey.txt

@@ -4,11 +4,44 @@ survey.*::
 	background with these options.
 +
 --
+	survey.namerev::
+		Boolean to show/hide `git name-rev` information for each
+		reported commit and the containing commit of each
+		reported tree and blob.
 	verbose::
 		This boolean value implies the `--[no-]verbose` option.
 	progress::
 		This boolean value implies the `--[no-]progress` option.
 	top::
 		This integer value implies `--top=<N>`, specifying the
 		number of entries in the detail tables.
+	showBlobSizes::
+		A non-negative integer value.  Requests details on the
+		<n> largest file blobs by size in bytes.  Provides a
+		default value for `--blob-sizes=<n>` in
+		linkgit:git-survey[1].
+	showCommitParents::
+		A non-negative integer value.  Requests details on the
+		<n> commits with the most number of parents.  Provides a
+		default value for `--commit-parents=<n>` in
+		linkgit:git-survey[1].
+	showCommitSizes::
+		A non-negative integer value.  Requests details on the
+		<n> largest commits by size in bytes.  Generally, these
+		are the commits with the largest commit messages.
+		Provides a default value for `--commit-sizes=<n>` in
+		linkgit:git-survey[1].
+	showTreeEntries::
+		A non-negative integer value.  Requests details on the
+		<n> trees (directories) with the most number of entries
+		(files and subdirectories).  Provides a default value
+		for `--tree-entries=<n>` in linkgit:git-survey[1].
+	showTreeSizes::
+		A non-negative integer value.  Requests details on the
+		<n> largest trees (directories) by size in bytes.  This
+		will set will usually be equal to the
+		`survey.showTreeEntries` set, but may be skewed by very
+		long file or subdirectory entry names.  Provides a
+		default value for `--tree-sizes=<n>` in
+		linkgit:git-survey[1].
 --

Documentation/git-survey.txt

@@ -32,6 +32,10 @@ OPTIONS
 --progress::
 	Show progress.  This is automatically enabled when interactive.
 
+--[no-]name-rev::
+	Print `git name-rev` output for each commit, tree, and blob.
+	Defaults to true.
+
 Ref Selection
 ~~~~~~~~~~~~~
 
@@ -59,6 +63,32 @@ only refs for the given options are added.
 --other::
 	Add notes (`refs/notes/`) and stashes (`refs/stash/`) to the set.
 
+Large Item Selection
+~~~~~~~~~~~~~~~~~~~~
+
+The following options control the optional display of large items under
+various dimensions of scale.  The OID of the largest `n` objects will be
+displayed in reverse sorted order.  For each, `n` defaults to 10.
+
+--commit-parents::
+	Shows the OIDs of the commits with the most parent commits.
+
+--commit-sizes::
+	Shows the OIDs of the largest commits by size in bytes.  This is
+	usually the ones with the largest commit messages.
+
+--tree-entries::
+	Shows the OIDs of the trees with the most number of entries.  These
+	are the directories with the most number of files or subdirectories.
+
+--tree-sizes::
+	Shows the OIDs of the largest trees by size in bytes.  This set
+	will usually be the same as the vector of number of entries unless
+	skewed by very long entry names.
+
+--blob-sizes::
+	Shows the OIDs of the largest blobs by size in bytes.
+
 OUTPUT
 ------
 
@@ -78,6 +108,11 @@ Reachable Object Summary
 The reachable object summary shows the total number of each kind of Git
 object, including tags, commits, trees, and blobs.
 
+CONFIGURATION
+-------------
+
+include::config/survey.txt[]
+
 GIT
 ---
 Part of the linkgit:git[1] suite