DAOS-18971 test: increate pool_space_metrics pool size

[daltonbohning]

Increase the pool size in pool_space_metrics.yaml since space pressure is causing lower performance.

Test-tag: TelemetryPoolSpaceMetrics
Test-repeat: 3

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is '1-./telemetry/pool_space_metrics.py:TelemetryPoolSpaceMetrics.test_telemetry_pool_space_metrics test timeout'
Status is 'In Progress'
Labels: 'ci_master_daily,testp2'
https://daosio.atlassian.net/browse/DAOS-18971

[daosbuild3]

Test stage Functional Hardware Medium MD on SSD completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18337/1/execution/node/799/log