feat(vmseries): VMSeries appgw backend pool association

[horiagunica]

Description

• Add possibility to attach vmseries interfaces to existing AppGW .
• This PR closes Add support for attaching interfaces to AppGW #88 .

Motivation and Context

• No current way to attach existing VMSeries interfaces to AppGW just like you would attach it to a regular Loadbalancer (from within the module).

How Has This Been Tested?

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.

[horiagunica]

/idempotence paths="examples/common_vmseries examples/common_vmseries_and_autoscale examples/dedicated_vmseries examples/dedicated_vmseries_and_autoscale examples/gwlb_with_vmseries examples/standalone_panorama examples/standalone_vmseries" tf_version="1.5 1.6 1.7 1.8"

Testing job ID: 10664590804
Job result: FAILURE
Job result: FAILURE

[acelebanski]

Looks good to me! 👍
However, we follow a principle in the examples to support all module variables out of the box. Can you also update the variables in the examples? If someone opts to use it, we want him to only add it to tfvars and that's it.

[horiagunica]

/idempotence paths="examples/common_vmseries examples/common_vmseries_and_autoscale examples/dedicated_vmseries examples/dedicated_vmseries_and_autoscale examples/gwlb_with_vmseries examples/standalone_panorama examples/standalone_vmseries" tf_version="1.5 1.6 1.7 1.8"

Testing job ID: 10681102373
Job result: FAILURE

[acelebanski]

Besides those little remarks regarding comments, looks great! Thanks! 👍