Add support for GitHub hosted large runners in cbi-sponsorships-api

GitHub hosted large runners have been added as a separate entity to the cbi-sponsorships-api, see

• https://github.com/eclipse-cbi/cbi/wiki#github-hosted-large-runner
• https://api.eclipse.org/cbi/sponsorships (field name is: "ghLargeRunners")

For testing purposes:

• only "Robert Bosch GmbH" has assigned one GitHub hosted large runner to the iot.ditto project.
• Every strategic member can assign 2 GitHub hosted large runners.

Please add this new field to the membership portal, so member organizations can see how many GitHub hosted large runners they have available/left (same as resource packs and dedicated agents).

Let me know if anything is unclear.