feat: add proposal for data support

docs/proposals/data.md

@@ -0,0 +1,82 @@
+# Data function support
+
+## Summary
+
+To provide mount data support for envd
+
+
+## Goals
+
+Design a *unified, declarative* interface and underlying architecture to provide dataset in the development environment in a *scalable way*
+
+
+Non-goals: 
+- Support Git-like version control for data
+
+## Common Scenarios
+
+### Possible sources
+- local files
+- Object storage (AWS S3)
+- NFS-like system (AWS EFS, AWS FSx for OpenZFS)
+- Block storage (Ceph)
+- HDFS
+- Lustre
+- API endpoint (http path)
+- SQL results
+- Other distributed fs (alluxio, juicefs)
+- Python SDK
+
+### Possible form
+- Images
+- Text
+- Embedding binarys
+- CSV
+
+### Access Pattern
+
+The access pattern of most dataset is write once, read multiple times, and concurrently. Therefore 
+
+### Possible versions/tags
+- Version by number, V1, V2, V3
+- Version by scale, sample dataset vs full dataset
+- Version by time, query range of user activity (7d, 30d) from feature store
+
+We can have a new standard on how to version the data like semver
+
+## Proposal
+
+Each version of dataset is immutable. By assuming the data is immutable, we can cache the data and make replication easily, to increase the read throughput in multiple ways.
+
+
+### Usage
+
+User need to create the dataset beforehand. Than declare mounting in the build.envd file.
+
+```
+envd data add -f mnist.yaml
+```
+
+User can create multiple dataset with the same name, but need to be different versions
+
+mnist.yaml
+```yaml=
+ApiVersion: V1alpha
+name: mnist
+version: "0.0.1-sample"
+sources:
+    - type: local # First source will be considered major source, others are the replication of this one
+      path: ~/.torch/mnist
+    - type: s3
+      path: xxx
+validation:
+    checksum:
+        - name: MD5
+          value: xxxx
+```
+
+build.envd
+```
+def data():
+    return [d.mount("mnist", target="./data")] # User can specify mount multiple datasets
+```