Commits 83dec5a712 and ff402ae11b taught vacuumdb to reuse
passwords instead of prompting repeatedly. However, the docs still
warn about repeated prompts, and this improvement was not applied
to clusterdb and reindexdb. This commit allows clusterdb and
reindexdb to reuse passwords just like vacuumdb does, and it
expunges the aforementioned warnings from the docs.
Reviewed-by: Gurjeet Singh, Zhang Mingli
Discussion: https://postgr.es/m/20230628045741.GA1813397%40nathanxps13
6d982e3b3b