fix(flux-system): Remove unused webhook config

This webhook is currently completely unused and only causes alerts,
therefore this shall be removed to make sure monitoring becomes green.

clusters/k8s01/flux-system/receiver.yaml

-apiVersion: notification.toolkit.fluxcd.io/v1beta1
-kind: Receiver
-metadata:
-  name: gitlab-receiver
-  namespace: flux-system
-spec:
-  events:
-  - Push Hook
-  - Tag Push Hook
-  resources:
-  - kind: GitRepository
-    name: flux-system
-  secretRef:
-    name: gitlab-webhook-token
-  type: gitlab

clusters/k8s01/flux-system/webhook-secret.yaml

-apiVersion: v1
-kind: Secret
-metadata:
-    name: gitlab-webhook-token
-    namespace: flux-system
-type: Opaque
-data:
-    token: ENC[AES256_GCM,data:OH3a73YY8Oii3q/gyzllsk2BX8phUMXe8nZNXjUT7CZk6UlWtXY3/c0rAZon3FBDaH1hKDhtsWVVdVcZ07kNOOtlc0ezdHkN5cD/fEfdPR8U+XttLsr+DQ==,iv:2wqK2ufJTV5MdRmDBKx+f+PxVGwoNox/MTJk4RXIml8=,tag:y/fvRyAYXdPKOCjBOsx3BA==,type:str]
-sops:
-    kms: []
-    gcp_kms: []
-    azure_kv: []
-    hc_vault: []
-    age: []
-    lastmodified: "2021-08-13T22:24:25Z"
-    mac: ENC[AES256_GCM,data:wbKWI4Qdjg8FYA56ASgchwZWT+yi6HT9ix1kwpH6wQ8hkVLTvNa2/tPQCILGcG/6DWGWtgQbKLp8wqp15MpRy5t/FqH2xTBXr6dY/5iDbvAgUA17QQI1w6xFIJoxdanthGFtrlZZTPz8YC9bAXpCN3Y1Icj4ZWgkzeqrn/QPd8Q=,iv:pm29MkED8RzetecXrrAOJtRQZmolKCLW1L5tF2hB+F0=,tag:VQym4XS8vbzWTaxydHYKJg==,type:str]
-    pgp:
-        - created_at: "2021-08-13T22:23:22Z"
-          enc: |
-            -----BEGIN PGP MESSAGE-----
-
-            hQIMA1u//sli4/n1ARAAyPUuDlqcn8uoyARE0anQfduu8UdylmAUBixoc7HqZy8t
-            E8psRdURyyMrqCinFQKiJIYaK5BAB80WNx5dw0tYz6HRmiojQVtyxcwle8edtiZO
-            jnw22USDiIfqNrYQd1lxE4pFKLKOwq897oXiLcwK4tdItCrlFWrklNetDZhEEfdB
-            /1Oz28lnHBsxmQyxYu8gsgQ2MekYMek1FTBP9ht/xWFH1GoASU27jeOxtUPre9QT
-            3Wf9NmgCPf0BW09S3DprUdjcphZ0qLp8xYkZ8FNyVWXAJ+EjoTO/AXbsNqAN8BF+
-            G8HGbV9QtXAUDT8zhF8nf7BVeKdTc5jhPaFlXOc9UwzdZfAuFwOw4Js34uIHC2lz
-            nVrn9qKlfsr3D9ab7Q7OoRnftXpbsnthCV5kkHWdnb5JbMkVxep001TVSbJoh97P
-            aTR4xCOcHvrDx9LR7ydXX0vMzki2k7zzJvcDtn9GwGAljz2M8epAi4BxEIPjyY52
-            yQMEErjFBUs48flB8sL/JIuBlxX5DlxekNuXBdTaoeYTN+AKgXEaH02FPgL8K3SY
-            mkc9bDEtTGo6PLpVaF/8qk1BRaoQ4yOrjASqrlzzbb8oZywSu39JvvwBesyBsXUs
-            RtRbop9hb5MYJ51010FBRMXuqbr2j9C4vMGgv4HtpOpKm0rmDFIB2uUoqfg6Pe7S
-            XgFd+cr4u3bHPsPnOgYxqhfG6aIj4cJyFmiBSH1yjcFUYBW+5i4pMeMYB+RQ/W2+
-            hfPYxkboXoZXwJbJYMhwh56UvaH8jcV1idzthoRNPngHG3WbYNwVarGHRScwhyU=
-            =tTg4
-            -----END PGP MESSAGE-----
-          fp: 9D02A9AD73EF7F3D5F657AC2B392F6EB325E8C50
-        - created_at: "2021-08-13T22:23:22Z"
-          enc: |-
-            -----BEGIN PGP MESSAGE-----
-
-            wcFMA7kpg2bgzVHcARAAjUgfdKLRkCovt4OvijlWqmOwemHvD5btBERoGvAR0Icu
-            xHcvUGdPtoMQ0JsZ71HT5Bt2efcmrYbBsUPSbXbbrWzqCx+JvO93oeBxY3AaVbzz
-            NmHOBY/VyTyzxIOxtW/Ob7VDAuDD4bv0NhtHJBcyqh9gdNXtZxTCbnyXvk6rbH7Q
-            k9HIw/A68QfR5rHppHmByBzc5OfuEvcGBInZgUUATUvYkEn2TfB4LLZ++L0jX8C6
-            2lqqURTOTZ2TVq8qijUXa+hNt4kYpHojySyUeNWTwCgAxAeMw++DGKciA5WzKTAY
-            bLALBcYMAh8lydJ//ISi3pyMvVsCjlN3BpM4VA/+0v5fkEtFd7GDMhuB1/CYza9n
-            YTo0tE9mZapoDmlIs6q7mDiD7xs4iNBeGpTU3vcDgImFZjNzHFWddN8s3ujzPZlD
-            7tDCcXh7mPFlWq0EUSy7DWbgbj945OuEKEplV/h0lVf93D67KpJEkaH/TnnYjXCQ
-            t51r+wAg8naC9Dfj3QHZt9xrmk3j3uMQBM6rzGMRvXqdwjSOH1uqULxTTVZzJryP
-            2LftqLxZrD5zdG8Gs0lYe+iwmHVhIOOfY1weLN3Y4yKbhk8aHUKFxhoTN/bPDBgk
-            sLBL4uqNSL1tku/ShZ+UOK1Rh82Q0wpUit+8OXi5biNGwkcEIwhpPpfm8yorL4bS
-            5gFWiuXXESNKa0ArSBrrLp5bncIMfIQ7wGohlKMVSf7NRzDFk49u+KC/10NBFaVP
-            0yRB+wxhQBMr8fxVAJsThqTkJr6FK6FD70/La76QSdJlmuJS19f5AA==
-            =l6ls
-            -----END PGP MESSAGE-----
-          fp: 286791FB6648539775DB31B8FCB98C2A3EC6F601
-    encrypted_regex: ^(data|stringData)$
-    version: 3.7.1