flagd sidecar injection fails PodSecurity "restricted" policy due to lowercase capabilities.drop value

[RTJoe]

Describe the bug

When the operator injects the flagdsidecar viagenerateBasicFlagdContainer(), pods are rejected in namespaces enforcing the Kubernetes PodSecurity restricted policy with the following error:

pods "" is forbidden: violates PodSecurity "restricted:v1.24":
unrestricted capabilities (container "flagd" must set securityContext.capabilities.drop=["ALL"])

## Root Cause

The `getSecurityContext()` function in `internal/common/flagdinjector/flagdinjector.go` sets `capabilities.drop` to `"all"` (lowercase):

```go
Capabilities: &corev1.Capabilities{
    Drop: []corev1.Capability{
        "all",  // ❌ lowercase
    },
},

The Kubernetes Pod Security Admission controller performs a case-sensitive string comparison against the constant capabilityAll = "ALL" in check_capabilities_restricted.go:

const capabilityAll = "ALL"

if c == capabilityAll {  // "all" != "ALL" → never matches

This means "all" is never recognised, so all pods with an injected flagd sidecar are blocked in restricted namespaces.

Steps to Reproduce
Create a namespace with pod-security.kubernetes.io/enforce: restricted
Deploy a pod with the openfeature.dev/enabled: "true" annotation
Pod is rejected with the error above
Expected Behaviour
The injected flagd sidecar should pass PodSecurity restricted admission. The intent is clearly to drop all capabilities (per the comment in the code), so "ALL" is the correct value.

Actual Behaviour
All pods with an injected flagd sidecar are rejected in restricted namespaces with unrestricted capabilities.

Fix
Change the drop value in getSecurityContext() to uppercase "ALL":

Capabilities: &corev1.Capabilities{
    Drop: []corev1.Capability{
        "ALL",  // ✅ matches capabilityAll constant in PSA
    },
},

The unit tests in flagdinjector_test.go (Test_getSecurityContext and getExpectedPod) also need updating to use "ALL".

A fix has been submitted in PR #804.

Environment
open-feature-operator: v0.8.9
Kubernetes: v1.24+
PodSecurity policy: restricted