[Task]: Add a flag to change GOTOOLCHAIN version used in the gateway builder to ap

[SavinduDimal]

Please select the area the issue is related to

CLI

Please select the aspect the issue is related to

Aspect/Configuration (Config files, settings, env vars, defaults)

Description

• Related issues: [Bug]: API Platform Controller gateway build fails when a policy requires a newer Go version #2796

• When building a wso2apip-api-gateway-1.1.0 image with jwt-auth@v1.2.2 using WSO2 API Platform Controller (ap) v0.8.0, the build fails.

• The underlying cause is a Go toolchain mismatch:

  • github.com/wso2/gateway-controllers/policies/jwt-auth@v1.2.2 declares go 1.26.5 in its go.mod.
  • The ghcr.io/wso2/api-platform/gateway-builder:1.1.0 image (the builder resolved for a 1.1.0 gateway) ships Go 1.26.2 with GOTOOLCHAIN=local.

• This has been already fixed for the gateway v1.2.0 release through fix(gateway-builder): force GOTOOLCHAIN=auto for go subprocesses #2798

• We need to release a new CLI patch version to set the GOTOOLCHAIN version via introducing a dedicated flag. (ex: ap gateway image build --go-toolchain go1.26.5)