Adds OR filters for epic boards

What does this MR do and why?

Adds OR filtering for labels on epic board list. Similar to previous change for epics resolver - !109813 (merged).

Related to #382969 (closed)

DB query

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/15113/commands/52500

SELECT "epics".* FROM "epics" LEFT OUTER JOIN "boards_epic_board_positions" ON "epics"."id" = "boards_epic_board_positions"."epic_id" AND "boards_epic_board_positions"."epic_board_id" = 1 WHERE "epics"."group_id" IN (SELECT "namespaces"."id" FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND (traversal_ids @> ('{9970}'))) AND "epics"."state_id" = 1 AND EXISTS (SELECT "label_links".* FROM "label_links" WHERE "label_links"."target_type" = 'Epic' AND "label_links"."target_id" = "epics"."id" AND "label_links"."label_id" IN (10690782, 10690741)) AND (EXISTS (SELECT "label_links".* FROM "label_links" WHERE "label_links"."target_type" = 'Epic' AND ("epics"."id" = "label_links"."target_id") AND "label_links"."label_id" = 11111311 LIMIT 1)) ORDER BY "boards_epic_board_positions"."relative_position" ASC NULLS LAST, epics.id DESC LIMIT 100 OFFSET 0

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

1. Enable the invite modal

   Feature.enable(:or_issuable_queries)

2. Sample query:

query {
  group(fullPath: "flightjs") {
    id
    epicBoards {
      nodes {
        id
        lists {
          nodes {
            id
            epics(filters: {or: {labelName: ["Phins", "Phint"]}}) {
              nodes {
                id
              }
            }
          }
        }
      }
    }
  }
}

MR acceptance checklist

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