install/kubernetes: allow extra helm resources

[bewing]

Allow additional aribitrary k8s resources to be added to the helm chart via the values file. This allows extension of the existing chart in a way that allows for the extension to be tracked via helm installation history, making rollbacks to earlier state easier than the current case, which involves performing a helm install and then adding/editing additional resources manually.

As an example use-case, you may wish to add additional ClusterRoles and ClusterRoleBindings to the cilium daemonset's service account to let an initContainer or sidecar container watch for LLDP traffic indicating a router, and configure CiliumBgpPeeringPolicies based on that data.

extraResources:
- |
  apiversion: rbac.authorization.k8s.io/v1
  kind: ClusterRole
  metadata:
    name: cilium-bgppeers
  rules:
  - apiGroups:
    - cilium.io
    resources:
    - ciliumbgppeerpolicies
    verbs:
    - get
    - list
    - create
    - patch
- |
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRoleBinding
  metadata:
    name: cilium-bgppeers
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: ClusterRole
    name: cilium-bgppeers
  subjects:
  - kind: ServiceAccount
    name: cilium
    namespace: kube-system

[maintainer-s-little-helper]

Commit 7d7153f does not match "(?m)^Signed-off-by:".

Please follow instructions provided in https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#developer-s-certificate-of-origin

[learnitall]

Hey thanks for the PR! This is an interesting idea, however I'm personally a bit opposed to it because it seems like an anti-pattern. The Cilium helm chart is built to install Cilium in a way that gets it up and running. If there are other resources that a user needs to apply alongside Cilium for their specific use case, and wants to take advantage of Helm's deployment features, it's my opinion that they should create a separate helm chart to do so. For example, a chart could be defined that includes the resources for a specific use-case and then specifies Cilium as a dependency. I'm definitely curious as to what other folks think though.

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