pgAdmin 4 commit: Use cheroot as default production server for pgAdmin4

Use cheroot as default production server for pgAdmin4. Fixes #5017

If DEBUG is true then we used the default flask server.

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=15c518f0f1a299b93676ea4e5d9d9de8a62c32c2
Author: Aditya Toshniwal <aditya.toshniwal@enterprisedb.com>

Modified Files
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docs/en_US/release_notes_4_17.rst |  1 +
requirements.txt                  |  1 +
web/pgAdmin4.py                   | 35 +++++++++++++++++++++++++----------
3 files changed, 27 insertions(+), 10 deletions(-)