Added doc for topic config comments rule

Author: sbuliarca

rules/msk_topic_config_comments.md

@@ -0,0 +1,75 @@
+# msk_topic_config_comments
+
+## Requirements
+
+Topic configurations expressed in milliseconds must have comments explaining the property and including the human-readable value.
+The comments can be placed after the property definition on the same line or on the line before the definition.
+
+For computing the human-readable values it considers the following:
+- 1 month has 30 days
+- 1 year has 365 days
+
+It currently checks the properties:
+- retention.ms: explanation must start with `keep data`
+- local.retention.ms: explanation must start with `keep data in primary storage`
+- max.compaction.lag.ms: explanation must start with `allow not compacted keys maximum`
+
+## Example
+
+### Good example
+
+```hcl
+# Good topic example with remote storage enabled
+resource "kafka_topic" "good_topic" {
+  name = "pubsub.good-topic"
+  replication_factor = 3
+  config = {
+    "remote.storage.enable" = "true"
+    "cleanup.policy"        = "delete"
+    # keep data in primary storage for 1 day
+    "local.retention.ms"    = "86400000"
+    "retention.ms"          = "2592000000" # keep data for 1 month 
+    "compression.type"      = "zstd"
+  }
+}
+
+# Good compacted topic
+resource "kafka_topic" "good topic" {
+  name               = "good_topic"
+  replication_factor = 3
+  config = {
+    "cleanup.policy"   = "compact"
+    "compression.type" = "zstd"
+    # allow not compacted keys maximum for 7 days
+    "max.compaction.lag.ms" = "604800000"
+  }
+}
+```
+
+### Bad examples
+
+```hcl
+# the value in the comment doesn't correspond to the actual value.
+resource "kafka_topic" "topic_wrong_retention_comment" {
+  name               = "topic_wrong_retention_comment"
+  replication_factor = 3
+  config = {
+    # keep data for 1 day
+    "retention.ms" = "172800000"
+  }
+}
+
+# the value is not commented at all
+resource "kafka_topic" "topic_without_retention_comment" {
+  name = "topic_without_retention_comment"
+  config = {
+    "local.retention.ms" = "86400000"
+  }
+}
+```
+
+## How To Fix
+
+The rule automatically fixes the comments. See the [requirements](#requirements)
+
+See [good example](#good-example)