Refactor file locking docs

There are two forms of file lock supported by GitLab. These were
documented in two different location. This merge request centralizes all
file locking documentation in a single location, and explains the
difference.

Detailed documentation has been added to explain how the `git-lfs` file
locking commands can be used not only for LFS files, but any file. This
is important for partial clone workflows involving large files.

doc/topics/git/lfs/index.md

@@ -111,69 +111,7 @@ To remove objects from LFS:
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/35856) in GitLab 10.5.
 
-The first thing to do before using File Locking is to tell Git LFS which
-kind of files are lockable. The following command will store PNG files
-in LFS and flag them as lockable:
-
-```shell
-git lfs track "*.png" --lockable
-```
-
-After executing the above command a file named `.gitattributes` will be
-created or updated with the following content:
-
-```shell
-*.png filter=lfs diff=lfs merge=lfs -text lockable
-```
-
-You can also register a file type as lockable without using LFS
-(In order to be able to lock/unlock a file you need a remote server that implements the LFS File Locking API),
-in order to do that you can edit the `.gitattributes` file manually:
-
-```shell
-*.pdf lockable
-```
-
-After a file type has been registered as lockable, Git LFS will make
-them read-only on the file system automatically. This means you will
-need to lock the file before editing it.
-
-### Managing Locked Files
-
-Once you're ready to edit your file you need to lock it first:
-
-```shell
-git lfs lock images/banner.png
-Locked images/banner.png
-```
-
-This will register the file as locked in your name on the server:
-
-```shell
-git lfs locks
-images/banner.png  joe   ID:123
-```
-
-Once you have pushed your changes, you can unlock the file so others can
-also edit it:
-
-```shell
-git lfs unlock images/banner.png
-```
-
-You can also unlock by ID:
-
-```shell
-git lfs unlock --id=123
-```
-
-If for some reason you need to unlock a file that was not locked by you,
-you can use the `--force` flag as long as you have a `maintainer` access on
-the project:
-
-```shell
-git lfs unlock --id=123 --force
-```
+TODO
 
 ## Troubleshooting