Add EmitWarningsOnPlaceholders("age") (#1997)

[shinyaaa]

Added EmitWarningsOnPlaceholders("age") to warn when an undefined GUC parameter is set for a placeholder named "age".

Warnings are issued when PostgreSQL starts and when SET statements are executed.

When PostgreSQL starts

2024-08-01 18:32:31.220 JST [2039799] WARNING: invalid configuration parameter name "age.invalid_parameter", removing it

When SET statement is executed

ERROR: invalid configuration parameter name "age.invalid_parameter"
DETAIL: "age" is a reserved prefix.

Regression tests were added.

[jrgemignani]

@shinyaaa There appears to be an issue with the build regression for this one :( Please look into it when you have an opportunity -

[github-actions[bot]]

This PR is stale because it has been open 60 days with no activity. Remove "Abondoned" label or comment or this will be closed in 14 days.

[github-actions[bot]]

This PR was closed because it has been stalled for further 14 days with no activity