pgsql: Replace use of deprecated Python module distutils.sysconfig

Replace use of deprecated Python module distutils.sysconfig

With Python 3.10, configure spits out warnings about the module
distutils.sysconfig being deprecated and scheduled for removal in
Python 3.12.  Change the uses in configure to use the module sysconfig
instead.  The logic stays the same.

Note that sysconfig exists since Python 2.7, so this moves the minimum
required version up from Python 2.6.

Discussion: https://www.postgresql.org/message-id/flat/c74add3c-09c4-a9dd-1a03-a846e5b2fc52%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e0e567a106726f6709601ee7cffe73eb6da8084e

Modified Files
--------------
config/python.m4               | 28 ++++++++++++++--------------
configure                      | 30 +++++++++++++++---------------
doc/src/sgml/installation.sgml |  4 ++--
3 files changed, 31 insertions(+), 31 deletions(-)