Add markdown block type

slack-base/src/main/java/com/hubspot/slack/client/models/blocks/Block.java

@@ -22,6 +22,7 @@
     @JsonSubTypes.Type(value = Image.class, name = Image.TYPE),
     @JsonSubTypes.Type(value = Input.class, name = Input.TYPE),
     @JsonSubTypes.Type(value = Section.class, name = Section.TYPE),
+    @JsonSubTypes.Type(value = Markdown.class, name = Markdown.TYPE),
   }
 )
 @JsonInclude(JsonInclude.Include.NON_EMPTY)

slack-base/src/main/java/com/hubspot/slack/client/models/blocks/BlockElementLengthLimits.java

@@ -11,7 +11,8 @@ public enum BlockElementLengthLimits {
   MAX_OPTION_GROUP_LABEL_LENGTH(75),
   MAX_OPTION_VALUE_LENGTH(75),
   MAX_CHECKBOXES_NUMBER(10),
-  MAX_RADIO_BUTTONS_NUMBER(10);
+  MAX_RADIO_BUTTONS_NUMBER(10),
+  MAX_MARKDOWN_LENGTH(12000);
 
   private final int limit;
 

slack-base/src/main/java/com/hubspot/slack/client/models/blocks/MarkdownIF.java

@@ -0,0 +1,50 @@
+package com.hubspot.slack.client.models.blocks;
+
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.annotation.JsonNaming;
+import com.google.common.base.Preconditions;
+import com.hubspot.immutables.style.HubSpotStyle;
+import org.immutables.value.Value.Check;
+import org.immutables.value.Value.Derived;
+import org.immutables.value.Value.Immutable;
+import org.immutables.value.Value.Parameter;
+
+@Immutable
+@HubSpotStyle
+@JsonNaming(PropertyNamingStrategies.SnakeCaseStrategy.class)
+public interface MarkdownIF extends Block {
+  String TYPE = "markdown";
+
+  /**
+   * The type of block. For a markdown block, type is always markdown.
+   * <br/><br/>
+   * Type: String
+   * <br/>
+   * Required: true
+   */
+  @Override
+  @Derived
+  default String getType() {
+    return TYPE;
+  }
+
+  /**
+   * The standard markdown-formatted text. Limit 12,000 characters max.
+   * <br/><br/>
+   * Type: String
+   * <br/>
+   * Required: true
+   */
+  @Parameter
+  String getText();
+
+  @Check
+  default void check() {
+    Preconditions.checkState(
+      getText().length() < BlockElementLengthLimits.MAX_MARKDOWN_LENGTH.getLimit(),
+      "Text length must be less than " +
+      BlockElementLengthLimits.MAX_MARKDOWN_LENGTH.getLimit() +
+      " characters"
+    );
+  }
+}