chore: publish documentation to docs.kcp.io

[embik]

We should look into publishing our docs (https://github.com/kcp-dev/api-syncagent/tree/main/docs) to docs.kcp.io. Currently, we have https://docs.kcp.io/kcp/, but it would be nice to have https://docs.kcp.io/api-syncagent/ as well.

The main challenge is figuring out how we integrate our local docs folder into the GitHub Pages that is hosting docs.kcp.io already.

[mirzakopic]

@embik @xrstf can you assign this to me please?

[embik]

/assign @mirzakopic