Implement allowed projects for MacOS Beta

What does this MR do?

Allows loading of a list of project URL prefixes that are allowed to participate in a beta program.

If a project prefix is not found within the list, a message similar to below is printed to the trace log and the job fails:

Why was this MR needed?

• Our current way of using registering tokens is tedious.
• The concurrency settings for the runner configuration are confusing when multiple Runners are configured. This will allow us to register just once as a instance Runner.

What's the best way to test this MR?

Create an allow list of projects:

# Create an allow list of projects
echo "/my-project/path" >> canary.project-allowlist

# Create a kubernetes secret with it
kubectl create secret generic orka-canary-project-allowlist --from-file=project-allowlist=canary.project-allowlist

Then modify the Helm values to make use of the allow list:

diff --git a/values-orka-canary.yaml b/values-orka-canary.yaml
index 0046bb9..9393c83 100644
--- a/values-orka-canary.yaml
+++ b/values-orka-canary.yaml
@@ -550,6 +551,7 @@ podLabels: {}
 ## mounted at /secrets.
 secrets:
   - name: orka-canary
+  - name: orka-canary-project-allowlist
 
 ## Additional config files to mount in the containers in `/configmaps`.
 ##
@@ -570,6 +572,8 @@ configMaps:
     Cores = 4
     Endpoint = "ORKA_API_ENDPOINT"
     Token = "ORKA_API_TOKEN"
+    BetaAllowedProjectsPath = "/secrets/project-allowlist"
 
       [Orka.ImageAliases]
       "macos-10.13-xcode-7" = "ork-10.13-7-202109061639"

What are the relevant issue numbers?