cli: Add -ignore-remote-version flag for init

When performing state migration to a remote backend target, Terraform
may fail due to mismatched remote and local Terraform versions. Here we
add the `-ignore-remote-version` flag to allow users to ignore this
version check when necessary.

internal/command/init.go

@@ -49,6 +49,7 @@ func (c *InitCommand) Run(args []string) int {
 	cmdFlags.BoolVar(&flagUpgrade, "upgrade", false, "")
 	cmdFlags.Var(&flagPluginPath, "plugin-dir", "plugin directory")
 	cmdFlags.StringVar(&flagLockfile, "lockfile", "", "Set a dependency lockfile mode")
+	cmdFlags.BoolVar(&c.Meta.ignoreRemoteVersion, "ignore-remote-version", false, "continue even if remote and local Terraform versions are incompatible")
 	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }
 	if err := cmdFlags.Parse(args); err != nil {
 		return 1
@@ -962,46 +963,49 @@ Usage: terraform [global options] init [options]
 
 Options:
 
-  -backend=true        Configure the backend for this configuration.
+  -backend=true           Configure the backend for this configuration.
 
-  -backend-config=path This can be either a path to an HCL file with key/value
-                       assignments (same format as terraform.tfvars) or a
-                       'key=value' format. This is merged with what is in the
-                       configuration file. This can be specified multiple
-                       times. The backend type must be in the configuration
-                       itself.
+  -backend-config=path    This can be either a path to an HCL file with key/value
+                          assignments (same format as terraform.tfvars) or a
+                          'key=value' format. This is merged with what is in the
+                          configuration file. This can be specified multiple
+                          times. The backend type must be in the configuration
+                          itself.
 
-  -force-copy          Suppress prompts about copying state data. This is
-                       equivalent to providing a "yes" to all confirmation
-                       prompts.
+  -force-copy             Suppress prompts about copying state data. This is
+                          equivalent to providing a "yes" to all confirmation
+                          prompts.
 
-  -from-module=SOURCE  Copy the contents of the given module into the target
-                       directory before initialization.
+  -from-module=SOURCE     Copy the contents of the given module into the target
+                          directory before initialization.
 
-  -get=true            Download any modules for this configuration.
+  -get=true               Download any modules for this configuration.
 
-  -input=true          Ask for input if necessary. If false, will error if
-                       input was required.
+  -input=true             Ask for input if necessary. If false, will error if
+                          input was required.
 
-  -no-color            If specified, output won't contain any color.
+  -no-color               If specified, output won't contain any color.
 
-  -plugin-dir          Directory containing plugin binaries. This overrides all
-                       default search paths for plugins, and prevents the
-                       automatic installation of plugins. This flag can be used
-                       multiple times.
+  -plugin-dir             Directory containing plugin binaries. This overrides all
+                          default search paths for plugins, and prevents the
+                          automatic installation of plugins. This flag can be used
+                          multiple times.
 
-  -reconfigure         Reconfigure the backend, ignoring any saved
-                       configuration.
+  -reconfigure            Reconfigure the backend, ignoring any saved
+                          configuration.
 
-  -migrate-state       Reconfigure the backend, and attempt to migrate any
-                       existing state.
+  -migrate-state          Reconfigure the backend, and attempt to migrate any
+                          existing state.
 
-  -upgrade=false       If installing modules (-get) or plugins, ignore
-                       previously-downloaded objects and install the
-                       latest version allowed within configured constraints.
+  -upgrade=false          If installing modules (-get) or plugins, ignore
+                          previously-downloaded objects and install the
+                          latest version allowed within configured constraints.
 
-  -lockfile=MODE       Set a dependency lockfile mode.
-                       Currently only "readonly" is valid.
+  -lockfile=MODE          Set a dependency lockfile mode.
+                          Currently only "readonly" is valid.
+
+  -ignore-remote-version  A rare option used for the remote backend only. See
+                          the remote backend documentation for more information.
 
 `
 	return strings.TrimSpace(helpText)