Enhance Mozilla SOPS Integration docs

The [Integration with Mozilla's sops](https://carvel.dev/kapp-controller/docs/v0.48.x/sops/)](https://carvel.dev/kapp-controller/docs/v0.48.x/sops/) docs jumps straight into a how-to instructions with no high level explanation of how the the integration works. The docs currently assume the reader already knows kapp-controller and Mozilla SOPS.

The SOPS doc page should have a small section added at the start of the doc that explains at a high level how the integration work. parts of this section are:

1. brief explanation of mozilla sops
3. brief explanation of the fetch / template / deploy life cycle of kapp-controller and where SOPS integrates into the lifecyle
4. Steps of the workflow for adding a secret via SOPS, the steps should not explain the how just the main steps. The rest of the doc will explain how to accomplish the steps. We are trying to help the users understand the sequence of steps they need to go through.
5. Steps of the workflow for updating a secret after it has been added, only high level steps not how to do it. The how should be explained in the rest of the doc.

Start with the linked Integration with Mozilla's sops documentation page and locate its source in the documentation site. Add a high-level overview covering SOPS, the kapp-controller fetch/template/deploy lifecycle, and the workflows for adding and updating secrets; keep detailed instructions in the existing sections and verify the rendered page.

Written by the indexing model from the issue text.