[PM-7014] Track MessagePack fork and turn off CI / recurring workflows (#3456)

* Remove messagepack submodule

* Migrate MessagePack fork to this repo

* Disable build CI

* Disable Renovate

* Disable Crowdin recurring job

* Address workflow linter errors

lib/MessagePack/README.md

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+# MessagePack
+
+[![Build Status][build status badge]][build status]
+
+A [MessagePack](https://msgpack.org/) encoder and decoder for `Codable` types.
+
+This functionality is discussed in Chapter 7 of
+[Flight School Guide to Swift Codable](https://flight.school/books/codable).
+
+## Requirements
+
+- Swift 4.2+
+
+## Usage
+
+### Encoding Messages
+
+```swift
+import MessagePack
+
+let encoder = MessagePackEncoder()
+let value = try! encoder.encode(["a": 1, "b": 2, "c": 3])
+// [0x83, 0xA1, 0x62, 0x02, 0xA1, 0x61, 0x01, 0xA1, 0x63, 0x03]
+```
+
+### Decoding Messages
+
+```swift
+import MessagePack
+
+let decoder = MessagePackDecoder()
+let data = Data(bytes: [0xCB, 0x40, 0x09, 0x21, 0xF9, 0xF0, 0x1B, 0x86, 0x6E])
+let value = try! decoder.decode(Double.self, from: data)
+// 3.14159
+```
+
+## Installation
+
+### Swift Package Manager
+
+Add the MessagePack package to your target dependencies in `Package.swift`:
+
+```swift
+import PackageDescription
+
+let package = Package(
+  name: "YourProject",
+  dependencies: [
+    .package(
+        url: "https://github.com/Flight-School/MessagePack",
+        from: "1.2.3"
+    ),
+  ]
+)
+```
+
+Then run the `swift build` command to build your project.
+
+### CocoaPods
+
+You can install `MessagePack` via CocoaPods,
+by adding the following line to your `Podfile`:
+
+```ruby
+pod 'MessagePack-FlightSchool', '~> 1.2.4'
+```
+
+Run the `pod install` command to download the library
+and integrate it into your Xcode project.
+
+> **Note**
+> The module name for this library is "MessagePack" ---
+> that is, to use it, you add `import MessagePack` to the top of your Swift code
+> just as you would by any other installation method.
+> The pod is called "MessagePack-FlightSchool"
+> because there's an existing pod with the name "MessagePack".
+
+## License
+
+MIT
+
+## Contact
+
+Mattt ([@mattt](https://twitter.com/mattt))
+
+[build status]: https://github.com/Flight-School/MessagePack/actions?query=workflow%3ACI
+[build status badge]: https://github.com/Flight-School/MessagePack/workflows/CI/badge.svg