Add support for stable and oldstable aliases

In scope of this release we introduce aliases for the go-version input. The stable alias instals the latest stable version of Go. The oldstable alias installs previous latest minor release (the stable is 1.19.x -> the oldstable is 1.18.x).

Stable

steps:
  - uses: actions/checkout@v3
  - uses: actions/setup-go@v3
    with:
      go-version: 'stable'
  - run: go run hello.go

OldStable

steps:
  - uses: actions/checkout@v3
  - uses: actions/setup-go@v3
    with:
      go-version: 'oldstable'
  - run: go run hello.go