feat: musl build of ffi engine

[markphelps]

Re: #141

• build flipt-engine-ffi with musl so it can run on alpine hosts
• remove rust-cross (uses docker to cross compile) and do it 'manually' on the build machines
• moves downloading of build ffi engines into dagger / Go when packaging the SDKs (easier to express in code than YAML)

trying this with the Go SDK first, it will create a new tag vX.X.X-musl for the Go SDK which will contain only the musl libs

Testing

After getting this to work (with using cross again), I tested this by creating a Dockerfile locally, and putting the built lib from the GitHub actions workflow in the correct place (flipt-client-go/ext/linux_arm64 as im on a m1 mac)

FROM golang:1.21.3-alpine

RUN apk add --no-cache build-base

WORKDIR /src

COPY . .

ENV FLIPT_URL="https://try.flipt.io"
ENV FLIPT_AUTH_TOKEN="flipt"
ENV LD_LIBRARY_PATH="/src/ext/linux_arm64:$LD_LIBRARY_PATH"

RUN go mod download

RUN go test ./...

It runs correctly, just fails since the data at https://try.flipt.io doesnt exist

 > [6/6] RUN go test ./...:                                                                                                                                             
5.069 --- FAIL: TestVariant (0.00s)                                                                                                                                     
5.069     evaluation_test.go:39:                                                                                                                                        
5.069         	Error Trace:	/src/evaluation_test.go:39                                                                                                              
5.069         	Error:      	Not equal:                                                                                                                              
5.069         	           	expected: "success"
5.069         	           	actual  : "failure"
5.069         	           	
5.069         	           	Diff:
5.069         	           	--- Expected
5.069         	           	+++ Actual
5.069         	           	@@ -1 +1 @@
5.069         	           	-success
5.069         	           	+failure
5.069         	Test:       	TestVariant
5.069     evaluation_test.go:40: 
5.069         	Error Trace:	/src/evaluation_test.go:40
5.069         	Error:      	Should be empty, but was invalid request: failed to get flag information default/flag1
5.069         	Test:       	TestVariant

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.38%. Comparing base (6190dd3) to head (c30436e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage   88.38%   88.38%           
=======================================
  Files          10       10           
  Lines        3686     3686           
=======================================
  Hits         3258     3258           
  Misses        428      428           

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[erka]

I tried the artifact on x86_64 alpine and works great.