feat: add caching and attestation verification

[vishal-chdhry]

Closes #3

test image: ghcr.io/vishal-chdhry/kyverno-notation-aws:test

NOTES:

1. PR is not this large, most of the changes are in go.sum and go.mod
2. This PR increased the size of binary (built using docker) from 59 MB to 77 MB
3. Condition key should not be enclosed in {{}} as kyverno will try to replace them. I am adding {{}} to the key in the request once it is recieved, conditions should be like this: key: creationInfo.licenseListVersion
4. The cache is cleared after every trust store and trust policy CRD change
5. Conditions are also cached so that 2 different conditions don't count as one.