fix(firewall): appending a rule without re-creating the whole ruleset (#2310)

* remove ForceNew: true from firewall rules resource

Signed-off-by: Ehsan Poursaeed <hsnprsd@gmail.com>

* add tests

Signed-off-by: Ehsan Poursaeed <hsnprsd@gmail.com>

* any -> interface{}

Signed-off-by: Ehsan Poursaeed <hsnprsd@gmail.com>

* add note on firewall rules doc

Signed-off-by: Ehsan Poursaeed <hsnprsd@gmail.com>

* fix: update ports in test to not interfere with API

Signed-off-by: Pavel Boldyrev <627562+bpg@users.noreply.github.com>

---------

Signed-off-by: Ehsan Poursaeed <hsnprsd@gmail.com>
Signed-off-by: Pavel Boldyrev <627562+bpg@users.noreply.github.com>
Co-authored-by: Pavel Boldyrev <627562+bpg@users.noreply.github.com>

Author: hsnprsd

docs/resources/virtual_environment_firewall_rules.md

@@ -9,6 +9,9 @@ subcategory: Virtual Environment
 
 Manages cluster-level, node-level or VM/container-level firewall rules.
 
+> **Note:** Before creating a new `proxmox_virtual_environment_firewall_rules` resource, verify that no rules already exist for the target (cluster, node, VM, or container).
+> If rules are already configured, import them first using the appropriate import command.
+
 ## Example Usage
 
 ```hcl