Set strong securityContext by default

[jemag]

Fixes #142

I have been using this securityContext with 3 different oauth-proxy so far and have not encountered any issues. Would still appreciate someone other than me testing it as well.

[pierluigilenoci]

@jemag This is a breaking change that cannot be introduced this way.
We must avoid breaking previous installations.

[jemag]

@pierluigilenoci Do you have any suggestions on how you would like this change to be introduced?
Should I have incremented the Major version instead of Minor?

This should not be breaking previous installations and has not in my testing, but let me know if you think I missed something.

[pierluigilenoci]

@jemag In reality, I don't feel very confident either to propose a possible solution.
I would prefer to have the opinion of the other maintainers as well.

@desaintmartin @tlawrie @NickMeves @JoelSpeed Would you be so kind as to give us an idea on how to deal with this?

[pierluigilenoci]

@jemag I just noticed that you still need to document all the new parameters you added inside the README.md.
Can you do this, please?

[morganchristiansson]

I applied these values and encountered no breaking changes. Thanks - seems like a great idea.