feat: Support t4g Graviton instance type (#1561)

Author: bliles

Diff for: README.md

@@ -91,7 +91,7 @@ To be able to support a number of use-cases the module has quite a lot configura
 
 #### ARM64 support via Graviton/Graviton2 instance-types
 
-When using the default example or top-level module, specifying an `instance_type` that matches a Graviton/Graviton 2 (ARM64) architecture (e.g. a1 or any 6th-gen `g` or `gd` type), the sub-modules will be automatically configured to provision with ARM64 AMIs and leverage GitHub's ARM64 action runner. See below for more details.
+When using the default example or top-level module, specifying an `instance_type` that matches a Graviton/Graviton 2 (ARM64) architecture (e.g. a1, t4g or any 6th-gen `g` or `gd` type), the sub-modules will be automatically configured to provision with ARM64 AMIs and leverage GitHub's ARM64 action runner. See below for more details.
 
 ## Usages
 
@@ -202,7 +202,7 @@ module "github-runner" {
 }
 ```
 
-**ARM64** support: Specify an `a1` or `*6g*` (6th-gen Graviton2) instance type to stand up an ARM64 runner, otherwise the default is x86_64.
+**ARM64** support: Specify an `a1`, `t4g` or `*6g*` (6th-gen Graviton2) instance type to stand up an ARM64 runner, otherwise the default is x86_64.
 
 Run terraform by using the following commands
 
@@ -347,7 +347,7 @@ The following sub modules are optional and are provided as example or utility:
 
 ### ARM64 configuration for submodules
 
-When not using the top-level module and specifying an `a1` or `*6g*` (6th-gen Graviton2) `instance_type`, the `runner-binaries-syncer` and `runners` submodules need to be configured appropriately for pulling the ARM64 GitHub action runner binary and leveraging the arm64 AMI for the runners.
+When not using the top-level module and specifying an `a1`, `t4g` or `*6g*` (6th-gen Graviton2) `instance_type`, the `runner-binaries-syncer` and `runners` submodules need to be configured appropriately for pulling the ARM64 GitHub action runner binary and leveraging the arm64 AMI for the runners.
 
 When configuring `runner-binaries-syncer`
 

Diff for: main.tf

@@ -5,7 +5,7 @@ locals {
   })
 
   s3_action_runner_url = "s3://${module.runner_binaries.bucket.id}/${module.runner_binaries.runner_distribution_object_key}"
-  runner_architecture  = substr(var.instance_type, 0, 2) == "a1" || substr(var.instance_type, 1, 2) == "6g" ? "arm64" : "x64"
+  runner_architecture  = substr(var.instance_type, 0, 2) == "a1" || substr(var.instance_type, 0, 3) == "t4g" || substr(var.instance_type, 1, 2) == "6g" ? "arm64" : "x64"
   github_app_parameters = {
     id         = module.ssm.parameters.github_app_id
     key_base64 = module.ssm.parameters.github_app_key_base64