Improve wording for TLS-related options

When configuring a SMTP sender, the user is prompted for an "Encryption
method" and given a drop-down list to choose from.  The list currently
contain "SSL", "TLS" and "None" which is a bit confusing given that TLS
is built on deprecated SSL and both refer to the same thing.

In this list, "SSL" actually mean TLS, and "TLS" actually mean StartTLS
(aka Opportunistic TLS).

Adjust wording to wake this more obvious.  The new wording match the one
used in Thunderbird when configuring connection security.

Signed-off-by: Romain Tartière <[email protected]>

public/pages/Emails/__tests__/SendersTableControls.test.tsx

@@ -56,7 +56,7 @@ describe('<SendersTableControls /> spec', () => {
       </MainContext.Provider>
     );
     fireEvent.click(utils.getByText('Encryption method'));
-    fireEvent.click(utils.getByText('TLS'));
+    fireEvent.click(utils.getByText('STARTTLS'));
     fireEvent.click(utils.getByText('None'));
     expect(onFiltersChange).toBeCalledWith({ encryptionMethod: ["start_tls", "none"] });
   });

public/pages/Emails/components/forms/CreateSenderForm.tsx

@@ -147,7 +147,7 @@ export function CreateSenderForm(props: CreateSenderFormProps) {
         style={{ maxWidth: '650px' }}
         helpText={
           <div>
-            SSL or TLS is recommended for security. To use either one, you must
+            SSL/TLS or STARTTLS is recommended for security. To use either one, you must
             enter each sender account's credentials to the OpenSearch
             keystore using the CLI.{' '}
             <EuiLink

public/utils/constants.ts

@@ -74,8 +74,8 @@ export const CHANNEL_TYPE = Object.freeze({
 };
 
 export const ENCRYPTION_TYPE = Object.freeze({
-  ssl: 'SSL',
-  start_tls: 'TLS',
+  ssl: 'SSL/TLS',
+  start_tls: 'STARTTLS',
   none: 'None',
 });