[BUG] no-rolling-update-strategy does not account for the default Strategy being RollingUpdate

[meganwalker-ibm]

Describe the bug
The no-rolling-update-strategy rule is looking for a DeploymentLike object to have a strategy.type field matching RollingUpdate|Rolling.

However the default value for this field is RollingUpdate making specifying it redundant: https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#strategy

However the rule is useful for ensuring we don't set a type of Recreate.

I think this rule would be better revised to consider a missing value as being a pass.

To Reproduce
Enable no-rolling-update-strategy.
Lint two deploymentLike objects. One that does not set a strategy. One that sets RolllingUpdate explicitly.
They are equivalent in effect, and so should be treated the same.

Sample YAML input
.kube-linter.yaml

checks:
  doNotAutoAddDefaults: true
  include:
    - no-rolling-update-strategy

sample.yaml

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app1
spec:
  strategy:
    type: Other
---
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
  name: app2
spec:
---
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
  name: app3
spec:
  strategy:
    type: RollingUpdate

Expected behavior
Only app1 should be identifies as violating this linting rule. app2 and app3 are directly equivalent to each other.

Additional context

[janisz]

@meganwalker-ibm You're right. Would you like to contribute a patch?
We need to tweek this regexp

kube-linter/pkg/builtinchecks/yamls/no-rolling-update-strategy.yaml

Line 12 in 7273651

strategyTypeRegex: "^(RollingUpdate|Rolling)$"

to allow empty value. You can also add your example to tests