Add an epp config flag to the InferencePool helm chart

[ahg-g]

The requirements are two fold:

1. Ability to select from a set of canned configurations.
2. Ability to provide new canned configurations to select from. This is important to allow other projects that customize EPP (like llm-d) to use the helm chart while providing custom configurations.

It seems the best way to do this is to define the configuration as a value that gets embedded in a configmap template that the chart creates.

An external values file can then be used to adds/overrides the configuration.

[ahg-g]

/triage accepted

[ahg-g]

/assign @nirrozenbaum