SONAR-14736 Highlight that installing plugins is manual

server/sonar-web/src/main/js/apps/marketplace/App.tsx

 import { Helmet } from 'react-helmet-async';
 import { FormattedMessage } from 'react-intl';
 import { Link } from 'react-router';
+import { Alert } from 'sonar-ui-common/components/ui/Alert';
 import DeferredSpinner from 'sonar-ui-common/components/ui/DeferredSpinner';
 import { translate } from 'sonar-ui-common/helpers/l10n';
 import {
           <div className="page-description">
             <p>{translate('marketplace.page.plugins.description')}</p>
             {currentEdition !== EditionKey.community && (
-              <p className="spacer-top">
+              <Alert className="spacer-top" variant="info">
                 <FormattedMessage
                   id="marketplace.page.plugins.description2"
                   defaultMessage={translate('marketplace.page.plugins.description2')}
                     )
                   }}
                 />
-              </p>
+              </Alert>
             )}
           </div>
         </header>

server/sonar-web/src/main/js/apps/marketplace/__tests__/__snapshots__/App-test.tsx.snap

       <p>
         marketplace.page.plugins.description
       </p>
-      <p
+      <Alert
         className="spacer-top"
+        variant="info"
       >
         <FormattedMessage
           defaultMessage="marketplace.page.plugins.description2"
             }
           }
         />
-      </p>
+      </Alert>
     </div>
   </header>
   <PluginRiskConsentBox
       <p>
         marketplace.page.plugins.description
       </p>
-      <p
+      <Alert
         className="spacer-top"
+        variant="info"
       >
         <FormattedMessage
           defaultMessage="marketplace.page.plugins.description2"
             }
           }
         />
-      </p>
+      </Alert>
     </div>
   </header>
   <PluginRiskConsentBox

sonar-core/src/main/resources/org/sonar/l10n/core.properties

 marketplace.risk_consent.title=Installation of plugins
 marketplace.risk_consent.description=Plugins are not provided by SonarSource and are therefore installed at your own risk. SonarSource disclaims all liability for installing and using such plugins. 
 marketplace.risk_consent.installation=You can install plugins directly from the list below after you acknowledge the risk.
-marketplace.risk_consent.action=I understand the risk.
+marketplace.risk_consent.action=I understand the risk
 
 plugin_risk_consent.title=Installation of plugins
 plugin_risk_consent.description=A plugin has been detected.