Re: introduce dynamic shared memory registry

Here's a new version of the patch set in which I've attempted to address
the feedback in this thread.  Note that 0001 is being tracked in a separate
thread [0], but it is basically a prerequisite for adding the documentation
for this feature, so that's why I've also added it here.

[0] https://postgr.es/m/20240112041430.GA3557928%40nathanxps13

-- 
Nathan Bossart
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