fix: add missing fields nameOverride and fullnameOverride

[maxime1907]

Fixes the missing fields in schema and values that are present in _helpers.tpl:

• fullnameOverride
• nameOverride

[maxime1907]

cc @consideRatio

[consideRatio]

Can you verify that the functionality described matches the behavior in this helm chart? This is copy pasted from jupyterhub/jupyterhub and some notes are related to that still, and the behavior in that helm chart is not standard as there were adjustments made to avoid introducing breaking changes when adding support for fullnameOverride and nameOverride.

• Validate documented claims
• Remove text about user pods that clearly is unrelated and review the notes in general, they probably don't make sense.

Alternatively, omit the descriptions. What is clear is that the schema should include the entries allowing them to be set, so just adding schemas without description in the schema is an improvement. I just don't want anything added to be misleading.

[consideRatio]

Thanks @maxime1907!!