Add Alpine variant to Dockerfile examples

Signed-off-by: J0WI <J0WI@users.noreply.github.com>

.examples/dockerfiles/imap/fpm-alpine/Dockerfile

@@ -0,0 +1,22 @@
+FROM nextcloud:fpm-alpine
+
+RUN set -ex; \
+    \
+    apk add --no-cache --virtual .build-deps \
+        $PHPIZE_DEPS \
+        imap-dev \
+        krb5-dev \
+        libressl-dev \
+    ; \
+    \
+    docker-php-ext-configure imap --with-kerberos --with-imap-ssl; \
+    docker-php-ext-install imap; \
+    \
+    runDeps="$( \
+        scanelf --needed --nobanner --format '%n#p' --recursive /usr/local/lib/php/extensions \
+            | tr ',' '\n' \
+            | sort -u \
+            | awk 'system("[ -e /usr/local/lib/" $1 " ]") == 0 { next } { print "so:" $1 }' \
+    )"; \
+    apk add --virtual .nextcloud-phpext-rundeps $runDeps; \
+    apk del .build-deps