chore(x2a): Add GitHub auth provider

[mareklibra]

Fixes: FLPATH-3085

Depends on (needs rebase):

• chores(x2a): Enable PostgreSQL in CI tests and add app-config.production.yaml #2178

Adding configuration to enable GitHub auth provider in our DEV environment.

To use it, make sure to set following environment variables:

export AUTH_GITHUB_CLIENT_ID=....
export AUTH_GITHUB_CLIENT_SECRET=...
yarn dev

There was attempt to add RBAC but this will need more work since @backstage/plugin-permission-backend fails to load.
This will be fixed in a follow-up, some debugging insight is included.

[rhdh-gh-app]

Unexpected Changesets

The following changeset(s) reference packages that have not been changed in this PR:

• /home/runner/work/rhdh-plugins/rhdh-plugins/workspaces/x2a/.changeset/jolly-lizards-heal.md: @red-hat-developer-hub/backstage-plugin-x2a-common

Note that only changes that affect the published package require changesets, for example changes to tests and storybook stories do not require changesets.

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@red-hat-developer-hub/backstage-plugin-x2a-backend	workspaces/x2a/plugins/x2a-backend	patch	v0.1.0
@red-hat-developer-hub/backstage-plugin-x2a	workspaces/x2a/plugins/x2a	patch	v0.1.0

[mareklibra]

Setting to draft to prevent accidental merge before the underlying PR

[mareklibra]

So far just an example.

The dev instance will be configured in a follow-up, failing in the mocked dev Backstage instances used so far.

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud