Add more configurability on Gateway as per #154

[Waterdrips]

Description

This adds the ability to set the Function RO Root FS setting and set min/max scaling for the function as per the request in #154

Signed-off-by: Alistair Hey alistair.hey@form3.tech Fixes: #154

How Has This Been Tested?

Tested by deploying to a new cluster and verifying the values are as expected

Checklist:

I have:

• [x] checked my changes follow the style of the existing code / OpenFaaS repos
• [x] updated the documentation and/or roadmap in README.md
• [x] read the CONTRIBUTION guide
• [x] signed-off my commits with git commit -s
• [ ] added unit tests

[Waterdrips]

Iv tested this on a new cluster, using ofc 0.14 (released this week) and verified that min scale set to 2 (using this setting) creates 2x function pods on successful build.

[Waterdrips]

this will be obsoleted by using the new Helm Chart (WIP)