Fix a typo in docs and in some warnings (#13538)

changelog.d/13538.doc

+Fix the doc and some warnings that were referring to the nonexistent `custom_templates_directory` setting (instead of `custom_template_directory`).
\ No newline at end of file

docs/templates.md

@@ -9,7 +9,7 @@ in, allowing them to specify custom templates:
 
 ```yaml
 templates:
-  custom_templates_directory: /path/to/custom/templates/
+  custom_template_directory: /path/to/custom/templates/
 ```
 
 If this setting is not set, or the files named below are not found within the directory,

synapse/config/account_validity.py

@@ -23,7 +23,7 @@ LEGACY_TEMPLATE_DIR_WARNING = """
 This server's configuration file is using the deprecated 'template_dir' setting in the
 'account_validity' section. Support for this setting has been deprecated and will be
 removed in a future version of Synapse. Server admins should instead use the new
-'custom_templates_directory' setting documented here:
+'custom_template_directory' setting documented here:
 https://matrix-org.github.io/synapse/latest/templates.html
 ---------------------------------------------------------------------------------------"""
 

synapse/config/emailconfig.py

@@ -53,7 +53,7 @@ LEGACY_TEMPLATE_DIR_WARNING = """
 This server's configuration file is using the deprecated 'template_dir' setting in the
 'email' section. Support for this setting has been deprecated and will be removed in a
 future version of Synapse. Server admins should instead use the new
-'custom_templates_directory' setting documented here:
+'custom_template_directory' setting documented here:
 https://matrix-org.github.io/synapse/latest/templates.html
 ---------------------------------------------------------------------------------------"""
 

synapse/config/sso.py

@@ -26,7 +26,7 @@ LEGACY_TEMPLATE_DIR_WARNING = """
 This server's configuration file is using the deprecated 'template_dir' setting in the
 'sso' section. Support for this setting has been deprecated and will be removed in a
 future version of Synapse. Server admins should instead use the new
-'custom_templates_directory' setting documented here:
+'custom_template_directory' setting documented here:
 https://matrix-org.github.io/synapse/latest/templates.html
 ---------------------------------------------------------------------------------------"""