Allow multiple SMTP Auth meganisms.

- Allow all SMTP Auth meganisms supported by Lettre.
- The config value order is leading and values can be separated by a
  comma ','
- Case doesn't matter, and invalid values are ignored.
- Warning is printed when no valid value is found at all.

.env.template

@@ -1,7 +1,7 @@
 ## Bitwarden_RS Configuration File
 ## Uncomment any of the following lines to change the defaults
-## 
-## Be aware that most of these settings will be overridden if they were changed 
+##
+## Be aware that most of these settings will be overridden if they were changed
 ## in the admin interface. Those overrides are stored within DATA_FOLDER/config.json .
 
 ## Main data folder
@@ -70,7 +70,7 @@
 ## Log level
 ## Change the verbosity of the log output
 ## Valid values are "trace", "debug", "info", "warn", "error" and "off"
-## Setting it to "trace" or "debug" would also show logs for mounted 
+## Setting it to "trace" or "debug" would also show logs for mounted
 ## routes and static file, websocket and alive requests
 # LOG_LEVEL=Info
 
@@ -184,7 +184,7 @@
 ## Authenticator Settings
 ## Disable authenticator time drifted codes to be valid.
 ## TOTP codes of the previous and next 30 seconds will be invalid
-## 
+##
 ## According to the RFC6238 (https://tools.ietf.org/html/rfc6238),
 ## we allow by default the TOTP code which was valid one step back and one in the future.
 ## This can however allow attackers to be a bit more lucky with there attempts because there are 3 valid codes.
@@ -210,6 +210,9 @@
 # SMTP_EXPLICIT_TLS=true # N.B. This variable configures Implicit TLS. It's currently mislabelled (see bug #851)
 # SMTP_USERNAME=username
 # SMTP_PASSWORD=password
+## Defaults for SSL is "Plain" and "Login" and nothing for Non-SSL connections.
+## Possible values: ["Plain", "Login", "Xoauth2"].
+## Multiple options need to be separated by a comma ','.
 # SMTP_AUTH_MECHANISM="Plain"
 # SMTP_TIMEOUT=15