Changes for deployment of VPN2 after rewrite to Go.

[MartinWeindel]

How to categorize this PR?

/area control-plane
/kind enhancement

What this PR does / why we need it:
The rewrite of the bash scripts to Go in vpn2 brings some changes in the deployment of the vpn-seed-server and vpn-shoot-client deployments.
These adjustments must be applied together with the new release of VPN2 containing the rewrite to Go (see PR gardener/vpn2#84)

Co-authored-by: @dergeberl
Co-authored-by: @hown3d
Co-authored-by: @mreiger

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Changes for deployment of VPN2 after rewrite to Go.

[gardener-prow]

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[gardener-prow]

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[gardener-prow]

PR needs rebase.

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