Add a link to OAuth 2 docs in help texts (#4034)

* Update installed_oauth_apps.jsx

* Update custom_integrations_settings.jsx

* Update confirm_integration.jsx

* Update installed_oauth_apps.jsx

* Update en.json

* Change FormattedMessage to FormattedHTMLMessage

* Fix proper coding of links in en.json

* Update en.json

webapp/components/admin_console/custom_integrations_settings.jsx

@@ -115,9 +115,9 @@ export default class WebhookSettings extends AdminSettings {
                         />
                     }
                     helpText={
-                        <FormattedMessage
+                        <FormattedHTMLMessage
                             id='admin.oauth.providerDescription'
-                            defaultMessage='When true, Mattermost can act as an OAuth 2.0 service provider allowing Mattermost to authorize API requests from external applications.'
+                            defaultMessage='When true, Mattermost can act as an OAuth 2.0 service provider allowing Mattermost to authorize API requests from external applications. See <a href="https://docs.mattermost.com/developer/oauth-2-0-applications.html" target="_blank">documentation</a> to learn more.'
                         />
                     }
                     value={this.state.enableOAuthServiceProvider}

webapp/components/integrations/components/confirm_integration.jsx

@@ -154,9 +154,9 @@ export default class ConfirmIntegration extends React.Component {
                 helpText = [];
                 helpText.push(
                     <p>
-                        <FormattedMessage
+                        <FormattedHTMLMessage
                             id='add_oauth_app.doneHelp'
-                            defaultMessage='Your OAuth 2.0 application has been set up. Please use the following Client ID and Client Secret when requesting authorization for your application.'
+                            defaultMessage='Your OAuth 2.0 application has been set up. Please use the following Client ID and Client Secret when requesting authorization for your application (see <a href="https://docs.mattermost.com/developer/oauth-2-0-applications.html">documentation</a> for further details).'
                         />
                     </p>
                 );

webapp/components/integrations/components/installed_oauth_apps.jsx

@@ -82,7 +82,21 @@ export default class InstalledOAuthApps extends React.Component {
                 helpText={
                     <FormattedMessage
                         id='installed_oauth_apps.help'
-                        defaultMessage='OAuth 2.0 Applications are available to everyone on your server.'
+                        defaultMessage='Create OAuth 2.0 applications to securely integrate bots and third-party applications with Mattermost. Please see {link} to learn more.'
+                        values={{
+                            link: (
+                                <a
+                                    target='_blank'
+                                    rel='noopener noreferrer'
+                                    href='https://docs.mattermost.com/developer/oauth-2-0-applications.html'
+                                >
+                                    <FormattedMessage
+                                        id='installed_oauth_apps.helpLink'
+                                        defaultMessage='documentation'
+                                    />
+                                </a>
+                            )
+                        }}
                     />
                 }
                 addText={