Upload crashes to collab directly (#8649)

This lets us run rustc_demangle on the backtrace, which helps the Slack
view significantly.

We're also now uploading files to digital ocean's S3 equivalent (with a
1 month expiry) instead of to Slack.

This PR paves the way for (but does not yet implement) sending this data
to clickhouse too.

Release Notes:

- N/A

crates/collab/src/api/slack.rs

@@ -0,0 +1,144 @@
+use serde::{Deserialize, Serialize};
+
+/// https://api.slack.com/reference/messaging/payload
+#[derive(Default, Clone, Serialize, Deserialize)]
+pub struct WebhookBody {
+    text: String,
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    blocks: Vec<Block>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    thread_ts: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    mrkdwn: Option<bool>,
+}
+
+impl WebhookBody {
+    pub fn new(f: impl FnOnce(Self) -> Self) -> Self {
+        f(Self::default())
+    }
+
+    pub fn add_section(mut self, build: impl FnOnce(Section) -> Section) -> Self {
+        self.blocks.push(Block::Section(build(Section::default())));
+        self
+    }
+
+    pub fn add_rich_text(mut self, build: impl FnOnce(RichText) -> RichText) -> Self {
+        self.blocks
+            .push(Block::RichText(build(RichText::default())));
+        self
+    }
+}
+
+#[derive(Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+/// https://api.slack.com/reference/block-kit/blocks
+pub enum Block {
+    #[serde(rename = "section")]
+    Section(Section),
+    #[serde(rename = "rich_text")]
+    RichText(RichText),
+    // .... etc.
+}
+
+/// https://api.slack.com/reference/block-kit/blocks#section
+#[derive(Default, Clone, Serialize, Deserialize)]
+pub struct Section {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    text: Option<Text>,
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    fields: Vec<Text>,
+    // fields, accessories...
+}
+
+impl Section {
+    pub fn text(mut self, text: Text) -> Self {
+        self.text = Some(text);
+        self
+    }
+
+    pub fn add_field(mut self, field: Text) -> Self {
+        self.fields.push(field);
+        self
+    }
+}
+
+/// https://api.slack.com/reference/block-kit/composition-objects#text
+#[derive(Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum Text {
+    #[serde(rename = "plain_text")]
+    PlainText { text: String, emoji: bool },
+    #[serde(rename = "mrkdwn")]
+    Markdown { text: String, verbatim: bool },
+}
+
+impl Text {
+    pub fn plain(s: String) -> Self {
+        Self::PlainText {
+            text: s,
+            emoji: true,
+        }
+    }
+
+    pub fn markdown(s: String) -> Self {
+        Self::Markdown {
+            text: s,
+            verbatim: false,
+        }
+    }
+}
+
+#[derive(Default, Clone, Serialize, Deserialize)]
+pub struct RichText {
+    elements: Vec<RichTextObject>,
+}
+
+impl RichText {
+    pub fn new(f: impl FnOnce(Self) -> Self) -> Self {
+        f(Self::default())
+    }
+
+    pub fn add_preformatted(
+        mut self,
+        build: impl FnOnce(RichTextPreformatted) -> RichTextPreformatted,
+    ) -> Self {
+        self.elements.push(RichTextObject::Preformatted(build(
+            RichTextPreformatted::default(),
+        )));
+        self
+    }
+}
+
+/// https://api.slack.com/reference/block-kit/blocks#rich_text
+#[derive(Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum RichTextObject {
+    #[serde(rename = "rich_text_preformatted")]
+    Preformatted(RichTextPreformatted),
+    // etc.
+}
+
+/// https://api.slack.com/reference/block-kit/blocks#rich_text_preformatted
+#[derive(Clone, Default, Serialize, Deserialize)]
+pub struct RichTextPreformatted {
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    elements: Vec<RichTextElement>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    border: Option<u8>,
+}
+
+impl RichTextPreformatted {
+    pub fn add_text(mut self, text: String) -> Self {
+        self.elements.push(RichTextElement::Text { text });
+        self
+    }
+}
+
+/// https://api.slack.com/reference/block-kit/blocks#element-types
+#[derive(Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum RichTextElement {
+    #[serde(rename = "text")]
+    Text { text: String },
+    // etc.
+}