Use Generation instead of ResourceVersion when computing the cache key

[ulucinar]

Description of your changes

The provider cache manager currently uses ProviderConfig.ResourceVersion when computing the cache keys. This PR changes it to ProviderConfig.Generation so that only ProviderConfig's spec updates will invalidate cache entries.

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.
• [ ] Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Validated the PR using the package index.docker.io/ulucinar/provider-aws-iam:v1.3.0-8dbbc58fbd82da76ef5f8f50c34aa75494964bbd and by modifying the spec of the ProviderConfig. Also via uptest here: https://github.com/crossplane-contrib/provider-upjet-aws/actions/runs/8470828375

[turkenf]

/test-examples="examples/rds/v1beta1/clusterroleassociation.yaml"