feat: add data sources for listing GitHub App installations in an organization

[atilsensalduz]

Resolves #2966
Resolves #2570

---

This PR introduces a new data source, github_app_installations, to enable listing all installed GitHub Apps within an organization. This addition enhances integration with existing resources such as github_app_installation_repository, providing better automation and management capabilities for GitHub App permissions.

What's New?
New Data Source: github_app_installations
Allows fetching all installed GitHub Apps in an organization:

data "github_organization_app_installations" "all_apps" {}

Example Use Case:
This data source can be integrated with the github_app_installation_repository resource to manage app permissions on specific repositories:

# Local value to find the correct app installation by slug
locals {
  # Find the index of the desired app by its slug
  app_index = index(
    data.github_organization_app_installations.all_apps.installations[*].slug,
    "desired-app-name"  # Replace with your actual app slug
  )
  
  # Get the app_id using the found index
  app_installation_id = data.github_organization_app_installations.all_apps.installations[local.app_index].id
}

# Link the repository to the app installation
resource "github_app_installation_repository" "some_app_repo" {
  installation_id = local.app_installation_id
  repository     = github_repository.some_repo.name
}

API Reference: https://docs.github.com/en/rest/orgs/orgs?apiVersion=2022-11-28#list-app-installations-for-an-organization

Related Issue: #2570

[github-actions]

👋 Hey Friends, this pull request has been automatically marked as stale because it has no recent activity. It will be closed if no further activity occurs. Please add the Status: Pinned label if you feel that this issue needs to remain open/active. Thank you for your contributions and help in keeping things tidy!

[deiga]

Hey 👋

Thank you for your contribution!

I've requested a few changes to make this fit into the provider even better :)

[deiga]

@atilsensalduz Please rebase and go through the comments

[atilsensalduz]

@atilsensalduz Please rebase and go through the comments

Hey @deiga , apologies for the late reply. I somehow missed this PR. Thanks so much for the review! I’ve worked through your suggestions.

[atilsensalduz]

Hi @deiga , I've changed the PR according to your suggestions. Could you please take a look again when you have time? Thanks in advance.

[stevehipwell]

@atilsensalduz could you please rebase this PR?

[stevehipwell]

Thanks for the PR @atilsensalduz, I've added a couple of comments. Could you also add support for single_file_paths, created_at & updated_at.

[stevehipwell]

@atilsensalduz this is looking good. Have you run the test locally, if so could you please attach a screenshot of the output?

[atilsensalduz]

@atilsensalduz this is looking good. Have you run the test locally, if so could you please attach a screenshot of the output?

Hi @stevehipwell, I've added test outputs as a screenshot.

[deiga]

Please rebase

[atilsensalduz]

Please rebase

Hey @deiga , I've rebased now.

[deiga]

Please run tests and linters and fix any issues

[atilsensalduz]

Please run tests and linters and fix any issues

Hey @deiga , I ran tests and linters, everything looks good in my local

[stevehipwell]

LGTM

[atilsensalduz]

Hey @stevehipwell , thanks for the suggestion to use getTestMeta(). I wasn't aware of this function. It was really helpful for adding a proper pre-check that skips the test when no GitHub App installations are found in the org, instead of relying on an implicit assumption.

=== RUN   TestAccGithubOrganizationAppInstallations
=== RUN   TestAccGithubOrganizationAppInstallations/basic
    data_source_github_organization_app_installations_test.go:18: Skipping because no GitHub App installations found in the test organization
--- PASS: TestAccGithubOrganizationAppInstallations (0.73s)
    --- SKIP: TestAccGithubOrganizationAppInstallations/basic (0.73s)
PASS
ok      github.com/integrations/terraform-provider-github/v6/github     1.445s

[stevehipwell]

Thanks @atilsensalduz, nearly there.

[stevehipwell]

LGTM

[atilsensalduz]

I've fixed linting issue. Could you please rerun the CI? @stevehipwell

[stevehipwell]

LGTM