Update kafka-connector chart for async invocations with backpressure

[welteki]

Description

Update kafka-connector chart for async invocations with back-pressure.

Add configuration parameters to support configuring a concurrency limit for async invocations.

Parameter	Description	Default
asyncInvocation	Invoke function asychronously and carry on processing the stream	false
asyncMaxInflight	Limit the number of inflight async invocations for the connector. A value of 0 indicates no concurrency limit.	0
asyncCallbackURL	Override the callback url passed as the X-Callback-URl header for async invocations to notify the connector an async invocation has completed.	""
natsURL	URL used to connect to nats to count the async concurrency. Override this value if you are using external nats.	nats://nats.openfaas:4222

Why is this needed?

• I have raised an issue to propose this change (required)

Who is this for?

What company is this for? Are you listed in the ADOPTERS.md file?

How Has This Been Tested?

Used the chart to test the connector-changes in my development cluster.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.