Add faasflow into the workflow engine list

[s8sg]

This PR adds FaaSFlow as a Workflow engine, primarily focused on OpenFaaS

FaaSFlow comes with a completely decoupled SDK which allows to build complex workflow as a DAG in Golang. Some of the main feature is

1. Support of Sub-DAG
2. Branching
3. Conditional Branching
4. ForEach Loop
5. Complete visibility for each state transition and many more

Thanks for creating the awesome list. Glad to see FaaSFlow listed here

Signed-off-by: s8sg [email protected]

[meirwah]

@s8sg can you fix conflicts ?