[Epic] Initial upgrade support

[joelanford]

Design docs

• Brief: Initial upgrade support
• RFC: Initial upgrade support

Precursor and related items

• Add support for honoring upgrade edges defined in the catalog #231
• Solver: Introduce constraints for "upgrade edges" #267
• Implement upgrade edges support #275

Task List

• Solver: Introduce variable sources for installed bundles #268
• Add ForceSemverUpgradeConstraints feature gate #395
• Update Operator CRD with UpgradeConstraintPolicy field #396
• Refactor legacy upgrade constraint semantics behind an interface #397
• Add semver upgrade edge generation support #398
• Respect .spec.upgradeConstraintPolicy #449
• Documentation for semver upgrade edge constraints support #470

[m1kola]

Added #449 since I realised that we do not cover .spec.upgradeConstraintPolicy in any other issue.

[m1kola]

Do we need to add an issue for documentation? Or is it being tracked elsewhere (I didn't manage find)?

[m1kola]

Added #470 for documentation.