Restructured working with PackageRevision guides

[Catalin-Stratulat-Ericsson]

This PR does 3 things

1. Firstly moves the package revision based guides into their personal subsection. as requested here Modifying repository guide #288 (comment)
2. Adds a general introduction section for package revision based guides much like the working with porch repositories has.
3. Takes out repeated content in the numerous guides related to working with package revisions and puts this content neatly in the _index.md introduction section of the section.

Its majority a refactor of the section. no real new content

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[efiacor]

/approve
/lgtm

[nephio-prow]

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