Fix casing of l7 proxy configuration to enable it by default

[ScheererJ]

How to categorize this PR?

/area networking
/kind bug

What this PR does / why we need it:
Fix casing of l7 proxy configuration to enable it by default.

Which issue(s) this PR fixes:
Fixes #257.

Special notes for your reviewer:
The usage of this helm option

gardener-extension-networking-cilium/charts/internal/cilium/charts/config/templates/configmap.yaml

Line 313 in 313bf58

{{- if .Values.global.l7Proxy }}

was using l7Proxy while it was introduced with the cilium 1.9.4 update as l7proxy in the configuration:

gardener-extension-networking-cilium/charts/internal/cilium/values.yaml

Line 462 in 313bf58

l7proxy:

Release note:

Cilium configuration option `enable-l7-proxy` is now enabled per default.

[axel7born]

/lgtm

[gardener-prow]

@ScheererJ: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-extension-networking-cilium-e2e-kind	5834efe	link	true	/test pull-extension-networking-cilium-e2e-kind

Full PR test history. Your PR dashboard. Command help for this repository.
Please help us cut down on flakes by linking this test failure to an open flake report or filing a new flake report if you can't find an existing one. Also see our testing guideline for how to avoid and hunt flakes.

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