Blocks Support: Create prefect_block resource - Update()

[parkedwards]

https://www.notion.so/prefect/Design-Block-support-in-the-Terraform-Provider-ae2ea25a18864de9b51b8aa06af9486b?pvs=4

resource "prefect_block" "datadog_api_key" {
	name = "datadog-api-key"
	type = "secret"
	data = jsonencode({
		value = var.datadog_api_key
	})
}

Located in internal/provider/resources/block.go

We'll need to add a Update() method on the pointer receiver for the BlockResource struct.

Afterwards we should be able to: update the data value in an existing block, eg. like in a key rotation scenario.

[mitchnielsen]

We moved things around, so the branch name from 0b1fb3d should no longer closet his one. Reopened.

[mitchnielsen]

Will wait for #174 before tackling this one.