docs: Document resource parsing with examples

[adwk67]

Description

Document the mapping of CRD resource definitions onto spark conf settings.
Fixes #294

Also removed spark.kubernetes.{executor|driver}.{request|limit}.memory as it does not appear in the spark code/branch-3.4.

CI: https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/spark-k8s-operator-it-custom/106/
CI: 🟢 https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/spark-k8s-operator-it-custom/108/

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

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1. Helm chart can be installed and deployed operator works
2. Integration tests passed (for non trivial changes)

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1. Code contains useful comments
2. (Integration-)Test cases added
3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

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1. Feature Tracker has been updated
2. Proper release label has been added

[adwk67]

Jenkins: 🟢 ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/spark-k8s-operator-it-custom/108

[sbernauer]

Thanks!