Allow triage-ops IssueSummary processor to support multiple projects

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What does this MR do and why?

This MR updates the IssueSummary processor so that the applicable? method checks against a list of allowed projects instead of being limited to gitlab-org/gitlab.

Currently, the processor only runs for the main GitLab project. By introducing an ALLOWED_PROJECTS constant (tracked in code), we make it easier to extend support to other GitLab projects in the future, while keeping changes reviewable through the MR process.

Default behaviour remains unchanged (gitlab-org/gitlab is still the only allowed project).

Expected impact & dry-runs

• No impact to current functionality since only gitlab-org/gitlab is allowed by default.