Add Architecture Naming Scheme RFC

Signed-off-by: Tristan Partin <tristan@neon.tech>

docs/rfcs/2025-04-23-architecture-naming-conventions.md

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+# Architecture Naming Scheme
+
+## Summary
+
+Neon computes are going to support multiple CPU architectures, including 64-bit
+x86 and ARM. Architecture naming schemes are fairly inconsistent, at least when
+it comes to these two architectures in particular. Sometimes 64-bit x86 is known
+as `amd64` and at other times `x86_64`. For 64-bit ARM, it's a similar story
+with `arm64` and `aarch64`.
+
+## Motivation
+
+Consistency when referring to these architectures across the platform in
+important not only so that everyone is on the same page, but also because we
+have architecture-dependent portions of the platform. One notable example is
+remote extensions. Remote extensions need to be compiled and packaged into
+compressed tarballs that are then downloaded by computes on demand. Downloading
+a tarball for the wrong architecture will cause `dlopen(3)` to fail when
+Postgres attempts to load the library. The compressed tarballs are located in an
+S3 bucket with object keys of the form
+`$BUILD_TAG/$ARCH/$PG_VERSION_NUM/${EXTENSION_NAME}.tar.zst` to mitigate the
+potential for failure. The build and deployment pipeline for remote extensions
+needs to be in lock step with the code in the compute that actually fetches
+remote extensions.
+
+## Impacted Components
+
+- Control Plane when persisting the target architecture in compute flags if
+  specified.
+- Austocaling when scheduling compute pods.
+- `compute_ctl` when downloading remote extensions.
+- Build and deployment pipeline for remote extensions.
+
+## Prior Art for CPU Architecture Names
+
+- [Rust](https://doc.rust-lang.org/std/env/consts/constant.ARCH.html)
+  - `x86_64`
+  - `arm64`
+- [Go](https://pkg.go.dev/internal/goarch#pkg-constants)
+  - `amd64`
+  - `arm64`
+- Kubernetes
+  - Because Kubernetes is written in Go, it inherits the naming scheme.
+
+Going all in on either the Rust naming scheme or the Go naming scheme can save
+us a branch when getting the architecture, so we should pick one and force the
+other side to conform.
+
+## Decision
+
+The heart of our platform is Kubernetes. We will inherit the Go naming
+scheme just like Kubernetes. This makes things easy for the autoscaling team
+when they do pod scheduling on nodes.