Create a new resource for webhook

[haipersuccor02]

This resource will allow to configure netbox webhook. This will allows us to configure webhook to Microsoft teams messages if new sites are being added to netbox or removed.

Test Result:

🚀 Netbox is up and running!
⌛ Startup acceptance tests on http://localhost:8001/
TF_ACC=1 go test -run TestAccNetBoxWebhook_basic -v -cover netbox/.go
=== RUN TestAccNetBoxWebhook_basic
=== PAUSE TestAccNetBoxWebhook_basic
=== CONT TestAccNetBoxWebhook_basic
--- PASS: TestAccNetBoxWebhook_basic (1.05s)
PASS
command-line-arguments coverage: 3.7% of statements
ok command-line-arguments 2.618s coverage: 3.7% of statements
TF_ACC=1 go test -run TestAccNetboxWebhook_update -v -cover netbox/.go
=== RUN TestAccNetboxWebhook_update
=== PAUSE TestAccNetboxWebhook_update
=== CONT TestAccNetboxWebhook_update
--- PASS: TestAccNetboxWebhook_update (1.43s)
PASS
command-line-arguments coverage: 4.2% of statements
ok command-line-arguments 2.810s coverage: 4.2% of statements
TF_ACC=1 go test -run TestAccNetboxWebhook_import -v -cover netbox/*.go
=== RUN TestAccNetboxWebhook_import
=== PAUSE TestAccNetboxWebhook_import
=== CONT TestAccNetboxWebhook_import
--- PASS: TestAccNetboxWebhook_import (0.92s)
PASS
command-line-arguments coverage: 3.7% of statements
ok command-line-arguments 2.294s coverage: 3.7% of statements

A dependency PR/MR for model is here : fbreckle/go-netbox#31

[fbreckle]

I rebased this and used the go-netbox client from the feature/webhooks branch as mentioned in fbreckle/go-netbox#31 (comment)

[haipersuccor02]

Thanks @fbreckle :)