Use upstream slack-go/slack again (#1018)

vendor/github.com/slack-go/slack/block_section.go

@@ -0,0 +1,42 @@
+package slack
+
+// SectionBlock defines a new block of type section
+//
+// More Information: https://api.slack.com/reference/messaging/blocks#section
+type SectionBlock struct {
+	Type      MessageBlockType   `json:"type"`
+	Text      *TextBlockObject   `json:"text,omitempty"`
+	BlockID   string             `json:"block_id,omitempty"`
+	Fields    []*TextBlockObject `json:"fields,omitempty"`
+	Accessory *Accessory         `json:"accessory,omitempty"`
+}
+
+// BlockType returns the type of the block
+func (s SectionBlock) BlockType() MessageBlockType {
+	return s.Type
+}
+
+// SectionBlockOption allows configuration of options for a new section block
+type SectionBlockOption func(*SectionBlock)
+
+func SectionBlockOptionBlockID(blockID string) SectionBlockOption {
+	return func(block *SectionBlock) {
+		block.BlockID = blockID
+	}
+}
+
+// NewSectionBlock returns a new instance of a section block to be rendered
+func NewSectionBlock(textObj *TextBlockObject, fields []*TextBlockObject, accessory *Accessory, options ...SectionBlockOption) *SectionBlock {
+	block := SectionBlock{
+		Type:      MBTSection,
+		Text:      textObj,
+		Fields:    fields,
+		Accessory: accessory,
+	}
+
+	for _, option := range options {
+		option(&block)
+	}
+
+	return &block
+}