Adapt extension Deployment's requests && limits and VPA

[ialidzhikov]

What this PR does / why we need it:
The 1st commit adapts the requests to the values according to the usage data. It also drops the cpu limit (see gardener/gardener#5627) and uses 5Gi as memory limit: 4 x 1.25Gi (max memory usage).
The 2nd commit enables VPA by default and sets controlledValues: RequestsOnly (see gardener/gardener#5638).

Which issue(s) this PR fixes:
N/A

Special notes for your reviewer:
N/A

Release note:

The extension Deployment resources and VPA are now adapted as follows:
- cpu limit is removed, memory limit is increased to 5Gi
- cpu and memory requests are reduced to 1m and 50Mi
- VPA is enabled by default in the extension chart values
- VPA's `controlledValues` is changed from `RequestsAndLimits` (default) to `RequestsOnly` 

[vlerenc]

Thank you @ialidzhikov.

/lgtm