Add support for "all" host type in package index tool definition

There is a catch-all "all" host type:
https://github.com/arduino/arduino-cli/blob/495a5f1a3d9d2f47b399329d6e6d91562fb683f8/arduino/cores/tools.go#L159

The package index JSON schema was missing support for this host type, resulting in spurious violations of rule IT0016.

Author: per1234

Diff for: etc/schemas/arduino-package-index-definitions-schema.json

@@ -1369,6 +1369,9 @@
               "validHost": {
                 "$comment": "https://github.com/arduino/arduino-cli/blob/cdbebe98f895c18146ea2607cfb706d002b01191/arduino/cores/tools.go#L144-L155",
                 "anyOf": [
+                  {
+                    "pattern": "^all$"
+                  },
                   {
                     "pattern": "^arm.*-linux-gnueabihf$"
                   },

Diff for: internal/project/packageindex/packageindexschemas_test.go

@@ -487,6 +487,10 @@ func TestPattern(t *testing.T) {
 		{"/packages/0/tools/0/systems/0/size", "foo", compliancelevel.Specification, assert.True},
 		{"/packages/0/tools/0/systems/0/size", "foo", compliancelevel.Strict, assert.True},
 
+		{"/packages/0/tools/0/systems/0/host", "all", compliancelevel.Permissive, assert.False},
+		{"/packages/0/tools/0/systems/0/host", "all", compliancelevel.Specification, assert.False},
+		{"/packages/0/tools/0/systems/0/host", "all", compliancelevel.Strict, assert.False},
+
 		{"/packages/0/tools/0/systems/0/host", "arm-linux-gnueabihf", compliancelevel.Permissive, assert.False},
 		{"/packages/0/tools/0/systems/0/host", "arm-linux-gnueabihf", compliancelevel.Specification, assert.False},
 		{"/packages/0/tools/0/systems/0/host", "arm-linux-gnueabihf", compliancelevel.Strict, assert.False},

Diff for: internal/rule/schema/schemadata/bindata.go

@@ -3904,6 +3904,9 @@ var _arduinoPackageIndexDefinitionsSchemaJson = []byte(`{
               "validHost": {
                 "$comment": "https://github.com/arduino/arduino-cli/blob/cdbebe98f895c18146ea2607cfb706d002b01191/arduino/cores/tools.go#L144-L155",
                 "anyOf": [
+                  {
+                    "pattern": "^all$"
+                  },
                   {
                     "pattern": "^arm.*-linux-gnueabihf$"
                   },