chore: rename sieve security to sieve filter

- Rename "Enable sieve security" to "Enable sieve filter"
- Use the translation function
- Add a small introduction for the feature

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

src/components/SieveAccountForm.vue

@@ -4,9 +4,12 @@
 -->
 <template>
 	<form id="sieve-form">
+		<p>
+			{{ t('mail', 'Sieve is a powerful language for writing filters for your mailbox. You can manage the sieve scripts in Mail if your email service supports it.') }}
+		</p>
 		<p>
 			<NcCheckboxRadioSwitch :checked.sync="sieveConfig.sieveEnabled">
-				{{ ('mail', 'Enable sieve security') }}
+				{{ t('mail', 'Enable sieve filter') }}
 			</NcCheckboxRadioSwitch>
 		</p>
 		<div v-if="sieveConfig.sieveEnabled">