Add documentation/examples on how to create/consume secrets for license files

[tnederlof]

Proposal

Add to each product chart README a recommendation to store license files as secrets and provide examples on how to create the secret and what values have to be set.

Reason

More and more customers are using license files for each of the products, and it is becoming the standard. Passing the license file contents in at helm install is clunky, and customers struggle with ensuring the format makes it into the container successfully.

[tnederlof]

@colearendt I am happy to take this on and add to the READMEs if you think its a good idea

[colearendt]

Sounds great! Related to #427