Service accounts

[Scroul]

Not sure if you want this level of configuration for service accounts but I am running the chart in a service mesh so need good control over the service account.

I can add/remove some parts if you feel that you only want a part of this.

With this keeping serviceAccount in values as it is now will put serviceAccountName: default so it will work as before if you do not use any of the new yaml values.

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[joejulian]

Would you mind opening an issue to associate with this that describes the symptoms you encounter with using a service mesh without this change? It would be really helpful for our docs team to be able to understand when and how this feature is used.

[Scroul]

I added #225 explaining how this can be used in a service mesh.