gitlab-ci: Build qthelp-format release documentation for cmake.org

Previously the qthelp-format release documentation on cmake.org was built manually.

Also add objects.inv to cmake.org html documentation, which was missing in !7144 (merged).

Backport: release

changed milestone to %3.23.1

added area:meta workflow:in-review labels

assigned to @brad.king

Warnings:

• Eligible for the 3.23.x branch.
• Eligible for the 3.22.x branch.

The warnings do not need to be fixed, but it is recommended to do so.

Do: stage

added workflow:nightly-testing label and removed workflow:in-review label

Do: merge

merged

mentioned in commit 76632f9f

mentioned in commit 5c429c5b

removed workflow:nightly-testing label

mentioned in commit 8070ff36