fix(ui-tests): resolve two flaky onboarding Cypress test failures

[Copilot]

Tests 3 and 5 of the onboarding suite were failing intermittently due to two independent race conditions — one involving the write-batcher leaking data across tests, the other a timing gap in the populator progress-bar check.

Test 3 — datatable-datapoints-sessions-0 contains non-zero value

Root cause: Countly's write-batcher (10 s flush interval) accumulates server_stats_data_points increments during test 2 (Entertainment demo). A single cy.dropMongoDatabase() in beforeEach drops the DB, but the in-flight batch flushes milliseconds later into the freshly-recreated database. By the time test 3 reaches the data-points page, all-apps.sessions is non-zero. Compounding the issue, el-table-column fixed="left" causes Element UI to render an extra shadow panel, producing two <span> elements with the same data-test-id; Cypress asserts on their combined text.

Fix: Drop the database twice in beforeEach, separated by a ~12 s wait, so any write-batcher flush that occurs after the first drop lands in already-dropped storage and the second drop clears it:

beforeEach(function() {
    cy.dropMongoDatabase();
    cy.wait(12000);         // let write-batcher flush into the dropped DB
    cy.dropMongoDatabase(); // wipe leaked data
    navigationHelpers.goToLoginPage();
});

Test 5 — geo countries total-sessions h2 doesn't contain "1000"

Root cause: checkPopulatorProgressBar() calls cy.elementExists() — a synchronous DOM lookup with zero retry timeout. If the progress bar hasn't appeared yet (app-creation API call still in flight when the check fires), isExists === false and the entire 120 s wait is silently skipped. The test then proceeds while the server is still processing populator sessions, so the aggregated geo total is < 1000.

Fix: Remove the conditional existence check and always wait for the bar to appear first, then wait for it to disappear:

const checkPopulatorProgressBar = () => {
    cy.get(`[data-test-id="${initialSetupPageElements.DATA_POP_PROGRESS_BAR}"]`, { timeout: 30000 })
        .should('exist');
    cy.get(`[data-test-id="${initialSetupPageElements.DATA_POP_PROGRESS_BAR}"]`, { timeout: 120000 })
        .should('not.exist');
};