Support for PostObject (#222)

Add support for [PostObject](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html)

- [x] routing PostObject properly
- [x] parsing multipart body
- [x] validating signature
- [x] validating policy
- [x] validating content length
- [x] actually saving data

Co-authored-by: trinity-1686a <trinity@deuxfleurs.fr>
Co-authored-by: Trinity Pointard <trinity.pointard@gmail.com>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/222
Reviewed-by: Alex <alex@adnab.me>
Co-authored-by: trinity-1686a <trinity.pointard@gmail.com>
Co-committed-by: trinity-1686a <trinity.pointard@gmail.com>

src/api/s3_xml.rs

@@ -289,6 +289,20 @@ pub struct VersioningConfiguration {
 	pub status: Option<Value>,
 }
 
+#[derive(Debug, Serialize, PartialEq)]
+pub struct PostObject {
+	#[serde(serialize_with = "xmlns_tag")]
+	pub xmlns: (),
+	#[serde(rename = "Location")]
+	pub location: Value,
+	#[serde(rename = "Bucket")]
+	pub bucket: Value,
+	#[serde(rename = "Key")]
+	pub key: Value,
+	#[serde(rename = "ETag")]
+	pub etag: Value,
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;