driver/kubernetes: add manifest-patch driver option

[abhay1999]

Add a generic manifest-patch driver option that accepts a jq
expression applied to the generated Deployment or StatefulSet
manifest after creation.

This allows users to set arbitrary manifest fields not exposed as
dedicated driver options, such as ownerReferences:

docker buildx create \
  --driver kubernetes \
  --driver-opt 'manifest-patch=.metadata.ownerReferences=[{"apiVersion":"actions.github.com/v1alpha1","kind":"EphemeralRunner","name":"runner-xyz","uid":"..."}]'

The jq expression is evaluated using github.com/itchyny/gojq, a
pure-Go jq implementation. The expression is validated at driver
initialization time. An error is returned if the expression is
invalid or produces no output.

Fixes #2626

[abhay1999]

@AkihiroSuda I've addressed your feedback and pushed an updated version:

• Replaced the bespoke ownerrefs option with a generic manifest-patch driver option that accepts any jq expression
• Used github.com/itchyny/gojq as the jq engine as you suggested
• The expression is applied to the generated Deployment/StatefulSet after creation by marshaling to JSON, running the jq query, and unmarshaling back
• DCO is passing, all tests pass
• Squashed into a single commit and updated the PR description

Example usage for the original ownerReferences use case:

--driver-opt 'manifest-patch=.metadata.ownerReferences=[{"apiVersion":"actions.github.com/v1alpha1","kind":"EphemeralRunner","name":"runner-xyz","uid":"..."}]'

Could you take another look when you get a chance?