Added ability to write to file

[Bullrich]

Added the ability to write the output of data to a file. It happens that if the output is too long GitHub Actions can not properly handle it and crashes.

In my case it is failing when calling the following code with the error Argument list too long

      - name: Write repo data
        run: echo "$DATA" > "$FILE"
        env:
          DATA: ${{ steps.pr.outputs.data }}
          FILE: outputs/${{ matrix.repo }}.json

This is after running on Polkadot which has more than a 100 PRs and produce a very big file.

Must be merged after #2