Bump provisioner in kcp chart

[ebensom]

Description

Changes proposed in this pull request:

• Bump provisioner to v20240521-bc0d8345 tag to include https://github.com/kyma-project/control-plane/pull/3438
• Remove L2/L3 operator related chart configuration
• Fix passing the gardener.defaultEnableIMDSv2 value to the provisioner as environment variable. After troubleshooting, it turned out that the envconfig packages tried to parse it having the APP_GARDENER_DEFAULT_ENABLE_IMD_SV2 underscore form.

Related issue(s)

https://github.tools.sap/kyma/backlog/issues/5553