In cPanel WHM EasyApache3 or EasyApache4, you can add GZIP compression server-wide, including new accounts, by adding the following to Service Configuration → Apache Configuration → Include Editor → Pre Virtualhost Include → All Versions:
# Enable GZIP Compression.
<IfModule mod_deflate.c>
SetOutputFilter DEFLATE
<IfModule mod_setenvif.c>
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html
# Don't compress images
SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary
</IfModule>
<IfModule mod_headers.c>
Header append Vary User-Agent env=!dont-vary
</IfModule>
</IfModule>
web