Add GitHub App support

This change adds the ability to use GitHub Apps to authenticate against the
GitHub API. This gives us a larger quota for API requests (15k vs 5k for PATs).

Also, each GitHub App has its own quota, whereas PATs share the same user quota.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

doc/github_credentials.md

@@ -4,16 +4,31 @@ The ```github``` config section holds credentials and API endpoint information f
 
 Tying the API endpoint info to the credentials allows us to use the same ```garm``` installation with both [github.com](https://github.com) and private deployments. All you have to do is to add the needed endpoint info (see bellow).
 
-Garm uses a [Personal Access Token (PAT)](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token) to create runner registration tokens, list current self hosted runners and potentially remove them if they become orphaned (the VM was manually removed on the provider).
+GARM has the option to use both [Personal Access Tokens (PAT)](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token) or a [GitHub App](https://docs.github.com/en/apps/creating-github-apps/registering-a-github-app/registering-a-github-app).
 
-From the list of scopes, you will need to select:
+
+If you'll use a PAT, you'll have to grant access for the following scopes:
 
 * ```public_repo``` - for access to a repository
 * ```repo``` - for access to a private repository
 * ```admin:org``` - if you plan on using this with an organization to which you have access
 * ```manage_runners:enterprise``` - if you plan to use garm at the enterprise level
+* ```admin:repo_hook``` - if you want to allow GARM to install webhooks on repositories (optional)
+* ```admin:org_hook``` - if you want to allow GARM to install webhooks on organizations (optional)
 
-The resulting token must be configured in the ```[[github]]``` section of the config. Sample as follows:
+If you plan to use github apps, you'll need to select the following permissions:
+
+* **Repository permissions**:
+  * ```Administration: Read & write```
+  * ```Metadata: Read-only```
+  * ```Webhooks: Read & write```
+* **Organization permissions**:
+  * ```Self-hosted runners: Read & write```
+  * ```Webhooks: Read & write```
+
+**Note** :warning:: Github Apps are not available at the enterprise level.
+
+The resulting credentials (app or PAT) must be configured in the ```[[github]]``` section of the config. Sample as follows:
 
 ```toml
 # This is a list of credentials that you can define as part of the repository
@@ -24,11 +39,27 @@ The resulting token must be configured in the ```[[github]]``` section of the co
 [[github]]
   name = "gabriel"
   description = "github token or user gabriel"
-  # This is a personal token with access to the repositories and organizations
-  # you plan on adding to garm. The "workflow" option needs to be selected in order
-  # to work with repositories, and the admin:org needs to be set if you plan on
-  # adding an organization.
-  oauth2_token = "super secret token"
+  # This is the type of authentication to use. It can be "pat" or "app"
+  auth_type = "pat"
+  [github.pat]
+     # This is a personal token with access to the repositories and organizations
+    # you plan on adding to garm. The "workflow" option needs to be selected in order
+    # to work with repositories, and the admin:org needs to be set if you plan on
+    # adding an organization.
+    oauth2_token = "super secret token"
+  [github.app]
+    # This is the app_id of the GitHub App that you want to use to authenticate
+    # with the GitHub API.
+    # This needs to be changed
+    app_id = 1
+    # This is the private key path of the GitHub App that you want to use to authenticate
+    # with the GitHub API.
+    # This needs to be changed
+    private_key_path = "/etc/garm/yourAppName.2024-03-01.private-key.pem"
+    # This is the installation_id of the GitHub App that you want to use to authenticate
+    # with the GitHub API.
+    # This needs to be changed
+    installation_id = 99
   # base_url (optional) is the URL at which your GitHub Enterprise Server can be accessed.
   # If these credentials are for github.com, leave this setting blank
   base_url = "https://ghe.example.com"