Add a new SetEnvFromFile directive that reads internal environment va…

[cisbiceanu]

mod_env: Add SetEnvFromFile directive

Add a new SetEnvFromFile directive that reads internal environment
variables from a file of "name=value" lines at configuration time.
Each entry is stored in the same per-directory table used by SetEnv,
so the values merge and reach r->subprocess_env identically and are
available to CGI, SSI, logging and other consumers.

The file is read once when the configuration is parsed. Blank lines
and '#' comments are ignored, surrounding whitespace is stripped, and
a line without '=' sets the variable to an empty string. Relative
paths are resolved against ServerRoot. A missing or unreadable file
fails configuration with an error, consistent with other file-backed
directives.

Because SetEnvFromFile and SetEnv write the same table, precedence
follows configuration order (last writer wins), matching existing
SetEnv semantics.

• modules/metadata/mod_env.c: Add add_env_module_vars_from_file() and
  the SetEnvFromFile (OR_FILEINFO, TAKE1) directive.
• docs/manual/mod/mod_env.xml: Document SetEnvFromFile.
• CHANGES: Add entry.
• test/pytest_suite: Add a SetEnvFromFile case to the mod_env test
  (vars.env fixture, fromfile.shtml, extra.conf.in, test_env.py).

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com