[PATCH] doc: vacuum_max_eager_freeze_failure_rate can be set by any user

Hi,

The description of vacuum_max_eager_freeze_failure_rate says:

This parameter can only be set in the postgresql.conf file or on the
server command line; but the setting can be overridden for individual
tables by changing the corresponding table storage parameter.

but the parameter is PGC_USERSET:

SET vacuum_max_eager_freeze_failure_rate = 0.5;
SET
SELECT context FROM pg_settings
WHERE name = 'vacuum_max_eager_freeze_failure_rate';
context
---------
user

I changed the wordings to match other vacuum related parameters.
Let me know if the attached patch makes sense.

Regards,
Afrah