Adds filesystem access example plugin

[JayJamieson]

Adding example plugin showing writing files to disk. Moved here from feedback in this PR

Do I need to update readme as well explaining usage?

[nilslice]

@JayJamieson thank you for this! maybe before we merge, it might be good to see how #26 helps this.. if we can instead use the documentation about this new package which should ease the usage of a reactor Go wasm module, then we may not need to have such specific instructions.

Could you test the new package in your module, and if it helps, rebase this branch off #26 (assuming its in main by then) and update the docs to what you think is best?

[JayJamieson]

Ah actually, this PR is not needed then sorry. I'll close since #26 better covers what my intention was. Thank you for taking the time to reply.

Thank you @mhmd-azeez for a much nicer implementation <3