Improve policy package deployment docs

[rdimaio]

Initial MD table for reference

Approach / columns	Ease of setup	Amount of work needed for new Rucio and new policy package versions	Extra external dependencies at runtime
Init container - from an index or Git repository	Easy		Index (e.g. PyPI) or Git registry (e.g. GitLab) in question (if a new policy package version is released)
Dockerfile with build arguments for policy package	Easy	- Building + hosting the image yourself - Rebuilding the image - Redeploying	Registry where you host the image (no more risk than what is already there, assuming your registry is as reliable as DockerHub)
Create secret and deploy via Flux	Medium	- Need to duplicate actual policy package content into Flux configuration	None
Cronjob that creates a secret policy and applies it	Medium	- Semi-automation of Flux secret approach	None

[rdimaio]

Pending rucio/containers#364 and rucio/helm-charts#221