Update apply documentation with the newly accepted -var/-var-file arguments (#3091)

Signed-off-by: Andrei Ciobanu <andrei.ciobanu@opentofu.org>

internal/command/apply.go

@@ -385,6 +385,15 @@ Options:
 
   -show-sensitive              If specified, sensitive values will be displayed.
 
+  -var 'foo=bar'               Set a variable in the OpenTofu configuration.
+                               This flag can be set multiple times.
+
+  -var-file=foo                Set variables in the OpenTofu configuration from
+                               a file.
+                               If "terraform.tfvars" or any ".auto.tfvars"
+                               files are present, they will be automatically
+                               loaded.
+
   -json                        Produce output in a machine-readable JSON format,
                                suitable for use in text editor integrations and
                                other automated systems. Always disables color.

website/docs/cli/commands/apply.mdx

@@ -94,6 +94,13 @@ The following options change how the apply command executes and reports on the a
   [walks the graph](../../internals/graph.mdx#walking-the-graph). Defaults to
   10\.
 
+- `-var 'foo=bar'` - Set a variable in the OpenTofu configuration.
+  This flag can be set multiple times.
+
+- `-var-file=foo` - Set variables in the OpenTofu configuration from a file.
+  If "terraform.tfvars" or any ".auto.tfvars" files are present, they will
+  be automatically loaded.
+
 - `-show-sensitive` - If specified, sensitive values will not be
   redacted in te UI output.