Downloader: Add forwarding to HTTP endpoint (#442)

* started with forwarding support in downloader

* Add missing files.

* Add missing files.

* Raise needed Go version

* More Go version bumping.

* Fix forwarding

* Go 1.21+ needed

* Make terminating forwarder more robust.

* Better var naming

* Remove dead code. Improve commentary.

* Prepare validation status adjustment.

* Move validations to functions to make them executable in a loop.

* Introduce validation mode flag (strict, unsafe)

.github/workflows/go.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.20.3
+          go-version: 1.21.0
 
       - name: Build
         run: go build -v ./cmd/...

.github/workflows/itest.yml

@@ -9,7 +9,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v3
         with:
-          go-version: 1.20.3
+          go-version: 1.21.0
 
       - name: Set up Node.js
         uses: actions/setup-node@v3

.github/workflows/release.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v3
         with:
-            go-version: '^1.20.3'
+            go-version: '^1.21.0'
 
       - name: Build
         run: make dist