Deprecate legacy Gitaly config methods

data/deprecations/14-8-gitaly-deprecate-legacy-config-options.yml

+- name: "Deprecate legacy Gitaly configuration methods"  # The name of the feature to be deprecated
+  announcement_milestone: "14.8"  # The milestone when this feature was first announced as deprecated.
+  announcement_date: "2022-02-22"  # The date of the milestone release when this feature was first announced as deprecated. This should almost always be the 22nd of a month (YYYY-MM-22), unless you did an out of band blog post.
+  removal_milestone: "15.0"  # The milestone when this feature is planned to be removed
+  removal_date: "2022-05-22"  # The date of the milestone release when this feature is planned to be removed. This should almost always be the 22nd of a month (YYYY-MM-22), unless you did an out of band blog post.
+  breaking_change: true  # If this deprecation is a breaking change, set this value to true
+  reporter: mjwood  # GitLab username of the person reporting the deprecation
+  body: |  # Do not modify this line, instead modify the lines below.
+    Using environment variables `GIT_CONFIG_SYSTEM` and `GIT_CONFIG_GLOBAL` to configure Gitaly is [deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/352609).
+    These variables are being replaced with standard [`config.toml` Gitaly configuration](https://docs.gitlab.com/ee/administration/gitaly/reference.html).
+
+    GitLab instances that use `GIT_CONFIG_SYSTEM` and `GIT_CONFIG_GLOBAL` to configure Gitaly should switch to configuring using
+    `config.toml`.
+# The following items are not published on the docs page, but may be used in the future.
+  stage: "Create"  # (optional - may be required in the future) String value of the stage that the feature was created in. e.g., Growth
+  tiers:  # (optional - may be required in the future) An array of tiers that the feature is available in currently.  e.g., [Free, Silver, Gold, Core, Premium, Ultimate]
+  issue_url: "https://gitlab.com/gitlab-org/gitlab/-/issues/352609"  # (optional) This is a link to the deprecation issue in GitLab
+  documentation_url: "https://docs.gitlab.com/ee/administration/gitaly/reference.html"  # (optional) This is a link to the current documentation page
+  image_url:  # (optional) This is a link to a thumbnail image depicting the feature
+  video_url:  # (optional) Use the youtube thumbnail URL with the structure of https://img.youtube.com/vi/UNIQUEID/hqdefault.jpg

doc/update/deprecations.md

@@ -809,6 +809,22 @@ The following `geo:db:*` tasks will be replaced with their corresponding `db:*:g
 
 **Planned removal milestone: 15.0 (2022-05-22)**
 
+### Deprecate legacy Gitaly configuration methods
+
+WARNING:
+This feature will be changed or removed in 15.0
+as a [breaking change](https://docs.gitlab.com/ee/development/contributing/#breaking-changes).
+Before updating GitLab, review the details carefully to determine if you need to make any
+changes to your code, settings, or workflow.
+
+Using environment variables `GIT_CONFIG_SYSTEM` and `GIT_CONFIG_GLOBAL` to configure Gitaly is [deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/352609).
+These variables are being replaced with standard [`config.toml` Gitaly configuration](https://docs.gitlab.com/ee/administration/gitaly/reference.html).
+
+GitLab instances that use `GIT_CONFIG_SYSTEM` and `GIT_CONFIG_GLOBAL` to configure Gitaly should switch to configuring using
+`config.toml`.
+
+**Planned removal milestone: 15.0 (2022-05-22)**
+
 ### Elasticsearch 6.8
 
 WARNING: