pgsql: Allocate enough shared string memory for stats of auxiliaryproc

Allocate enough shared string memory for stats of auxiliary processes.

This fixes a bug whereby the st_appname, st_clienthostname, and
st_activity_raw fields for auxiliary processes point beyond the end of
their respective shared memory segments. As a result, the application_name
of a backend might show up as the client hostname of an auxiliary process.

Backpatch to v10, where this bug was introduced, when the auxiliary
processes were added to the array.

Author: Edmund Horner
Reviewed-by: Michael Paquier
Discussion:
https://www.postgresql.org/message-id/CAMyN-kA7aOJzBmrYFdXcc7Z0NmW%2B5jBaf_m%3D_-77uRNyKC9r%3DA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/811969b218ac2e8030dfbbb05873344967461618

Modified Files
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src/backend/postmaster/pgstat.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)