DAOS-19202 client: Fix cont_create use-after-frees

[liw]

Calling daos_cont_create_with_label may result in use-after-frees when
underlying tasks reinitialize:

cont_prop  ev        Use-after-free
----------------------------------------------------------------
NULL       non-NULL  merged_props in daos_cont_create
RF         non-NULL  merged_props in daos_cont_create_with_label

This patch refactors daos_cont_create_with_label and daos_cont_create to
free properties they allocate in task completion callbacks.

Features: container

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 'Use-after-free issues in daos_cont_create_with_label when events are used'
Status is 'In Progress'
https://daosio.atlassian.net/browse/DAOS-19202

[daosbuild3]

Test stage NLT completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18515/3/testReport/

[daosbuild3]

Test stage Functional Hardware Large 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-18515/3/execution/node/1401/log

[daosbuild3]

Test stage Functional Hardware Medium MD on SSD completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18515/3/testReport/

[daosbuild3]

Test stage NLT completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18515/4/testReport/

[daosbuild3]

Test stage Functional Hardware Large 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-18515/4/execution/node/1167/log

[daosbuild3]

Test stage Functional Hardware Medium MD on SSD completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18515/4/testReport/