Document the new DEFAULT_DELETE_BRANCH_AFTER_MERGE default (#608)

Documents https://github.com/go-gitea/gitea/pull/39975 for main, which changes the default of `DEFAULT_DELETE_BRANCH_AFTER_MERGE` to `true`.

Reviewed-on: https://gitea.com/gitea/docs/pulls/608
Reviewed-by: Lunny Xiao <[email protected]>

docs/administration/config-cheat-sheet.md

@@ -179,7 +179,7 @@ In addition, there is _`StaticRootPath`_ which can be set as a built-in at build
 - `POPULATE_SQUASH_COMMENT_WITH_COMMIT_MESSAGES`: **false**: In default squash-merge messages include the commit message of all commits comprising the pull request.
 - `ADD_CO_COMMITTER_TRAILERS`: **true**: Add co-authored-by and co-committed-by trailers to merge commit messages if committer does not match author.
 - `RETARGET_CHILDREN_ON_MERGE`: **true**: Retarget child pull requests to the parent pull request branch target on merge of parent pull request. It only works on merged PRs where the head and base branch target the same repo.
-- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **false**: Set the default value for "Delete pull request branch after merge by default" for new repositories.
+- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **true**: Set the default value for "Delete pull request branch after merge by default" for new repositories.
 - `DEFAULT_TITLE_SOURCE`: **auto**: Default source for the pull request title when opening a new PR. Valid options:
   - `first-commit`: Uses the oldest commit's summary as the title. If there are multiple commits, still uses the first commit's message.
   - `auto`: Uses the commit's summary when the PR contains a single commit; when there are multiple commits, converts the branch name into a human-readable title by normalizing separators and casing.

i18n/zh-cn/docs/current/administration/config-cheat-sheet.md

@@ -141,7 +141,7 @@ aliases:
 - `POPULATE_SQUASH_COMMENT_WITH_COMMIT_MESSAGES`: **false**: 在默认的 squash 合并消息中，包括构成拉取请求的所有提交的提交消息。
 - `ADD_CO_COMMITTER_TRAILERS`: **true**: 如果提交者与作者不匹配，在合并提交消息中添加`co-authored-by`和`co-committed-by`标记。
 - `RETARGET_CHILDREN_ON_MERGE`: **true**: 当父合并请求被合并时，将子合并请求重新定向到父合并请求的目标分支。仅适用于头分支和基分支指向同一仓库的已合并合并请求。
-- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **false**: 为新仓库设置"合并后默认删除合并请求分支"的默认值。
+- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **true**: 为新仓库设置"合并后默认删除合并请求分支"的默认值。
 
 ### 仓库 - 工单 (`repository.issue`)
 

i18n/zh-tw/docs/current/administration/config-cheat-sheet.md

@@ -142,7 +142,7 @@ aliases:
 - `POPULATE_SQUASH_COMMENT_WITH_COMMIT_MESSAGES`: **false**: 在預設的 squash 合併消息中，包括構成拉取請求的所有提交的提交消息。
 - `ADD_CO_COMMITTER_TRAILERS`: **true**: 如果提交者與作者不匹配，在合併提交消息中添加`co-authored-by`和`co-committed-by`標記。
 - `RETARGET_CHILDREN_ON_MERGE`: **true**: 當父合併請求被合併時，將子合併請求重新定向到父合併請求的目標分支。僅適用於頭分支和基分支指向同一儲存庫的已合併合併請求。
-- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **false**: 為新儲存庫設定"合併後預設刪除合併請求分支"的預設值。
+- `DEFAULT_DELETE_BRANCH_AFTER_MERGE`: **true**: 為新儲存庫設定"合併後預設刪除合併請求分支"的預設值。
 
 ### 儲存庫 - 工單 (`repository.issue`)