Greengrass v2 IPC Connection and Sample

[Kriechi]

This PR incorporates the recommended code pieces or IPCUtils from the official documentation page:
https://docs.aws.amazon.com/greengrass/v2/developerguide/interprocess-communication.html#ipc-requirements

We can simplify and streamline the whole setup and user-facing API by moving and fully integrating this code snippet / requirement from the documentation page into the awsiotsdk and providing a wrapper function.

The new awsiot.greengrasscoreipc.connect() function is "ready to use" without function arguments, but can also be supplied with arguments to customize the behaviour of the returned GreengrassCoreIPCClient. You can also pass in a LifecycleHandler, which the original documentation-based code snippet did not explain or provide.

The new example ipc_greengrass.py is a simple GGv2 component which periodically publishes small json-based telementry events to IoT Core - throught the GGv2 IPC connection layer. The necessary component recipe snippets are included in the comment block at the top of the sample.

This PR includes 3 commits (feel free to cherry pick):

• IPC connection management and an GGv2 sample component
• greengrasscoreipc documentation RST files
• a fresh rendering of all docs pages (including the newly added ones)

Follow-up action items after this PR is merged and a new awsiotsdk version is released:

• update the docs here to bump the awsiotsdk version
• remove the IPCUtils code from the docs
• simplify the publishing example in the docs here and the docs here and the docs here

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Kriechi]

@JonathanHenson small thought: does it makes sense to have the port number as argument here? Connecting to a local socket probably ignore the port anyway?

edit: I removed the port and renamed the hostname argument to ipc_socket.

[JonathanHenson]

@JonathanHenson small thought: does it makes sense to have the port number as argument here? Connecting to a local socket probably ignore the port anyway?

edit: I removed the port and renamed the hostname argument to ipc_socket.

port is unused if you use a local domain socket, but leaving port in with a default makes sense if you want to be able to support other socket types or transports in the future. One thing though, I think we're supposed to be using kwargs** everywhere for backwards compat purposes, let's have @graebm have a look and if he's fine with this, merge it.