[api] allow specifying componentOverride for cluster creation REST call

**What would you like to be added? / User Story**:
As a KKP administration creating clusters using API based automation,

I would like to provide compoentOverride settings in cluster spec as part of cluster creation REST call itself.

We create user clusters which are pretty big and also operator heavy. We have always seen that the prometheus pod as well as APIserver pods needs extra resources than what is given by default as part of cluster creation. So we would like the ability to specify such options (and all the other options available in componentOverride section of cluster spec) via json payload sent for creation of cluster.

The same option should also be accepted as part of subsequent cluster update call as well and should be reconciled.

Start by tracing the cluster creation REST call and subsequent cluster update call, then inspect how componentOverride is represented in the cluster spec JSON. Verify that both request paths accept the componentOverride settings and that the supplied values are reconciled.

Written by the indexing model from the issue text.