patch 9.1.1177: filetype: tera files not detected

Problem:  filetype: tera files not detected
Solution: detect '*.tera' files as tera filetype,
          include a simple filetype plugin
          (MuntasirSZN)

closes: #16806

Signed-off-by: MuntasirSZN <muntasir.joypurhat@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/tera.vim b/runtime/ftplugin/tera.vim
new file mode 100644
index 0000000..47636f2
--- /dev/null
+++ b/runtime/ftplugin/tera.vim
@@ -0,0 +1,13 @@
+" Vim filetype plugin file
+" Language:             Tera
+" Maintainer:           Muntasir Mahmud <muntasir.joypurhat@gmail.com>
+" Last Change:          2025 Mar 06
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal commentstring={#\ %s\ #}
+
+let b:undo_ftplugin = "setlocal commentstring<"