Respect expires header when checking for new version

It was called to many times and acted similar to a DOS attack.

app/src/main/java/org/schabi/newpipe/NewVersionManager.kt

@@ -0,0 +1,28 @@
+package org.schabi.newpipe
+
+import java.time.Instant
+import java.time.ZonedDateTime
+import java.time.format.DateTimeFormatter
+
+class NewVersionManager {
+
+    fun isExpired(expiry: Long): Boolean {
+        return Instant.ofEpochSecond(expiry).isBefore(Instant.now())
+    }
+
+    /**
+     * Coerce expiry date time in between 6 hours and 72 hours from now
+     *
+     * @return Epoch second of expiry date time
+     */
+    fun coerceExpiry(expiryString: String?): Long {
+        val now = ZonedDateTime.now()
+        return expiryString?.let {
+
+            var expiry = ZonedDateTime.from(DateTimeFormatter.RFC_1123_DATE_TIME.parse(expiryString))
+            expiry = maxOf(expiry, now.plusHours(6))
+            expiry = minOf(expiry, now.plusHours(72))
+            expiry.toEpochSecond()
+        } ?: now.plusHours(6).toEpochSecond()
+    }
+}