[DOCS] Document event_match_type option for master and minion configuration files

Description

This was discovered as part of working on #58112

How is event_match_type used, when listed in the minion and master config files?

https://github.com/saltstack/salt/blob/8afbb8e00556e0d491f6052308469e9f4a0c7672/conf/minion#L929-L932

Suggested Fix

Define how it is used, and what the available values mean, at least somewhere in the master and minion docs (*.rst files)

• startswith
• endswith
• find
• regex
• fnmatch

Type of documentation

• minion/master configuration files
• Salt Documentation (.rst) for master/minion configuration files

Location or format of documentation

Master:

• https://github.com/saltstack/salt/blob/master/conf/master
• https://github.com/saltstack/salt/blob/master/doc/ref/configuration/master.rst
  • Rendered HTML: https://docs.saltstack.com/en/latest/ref/configuration/master.html

Minion:

• https://github.com/saltstack/salt/blob/master/conf/minion
• https://github.com/saltstack/salt/blob/master/doc/ref/configuration/minion.rst
  • Rendered HTML: https://docs.saltstack.com/en/latest/ref/configuration/minion.html

Additional context

15:28 $ grep -nr "event_match_type"| grep -v "Binary file"
salt/utils/event.py:450:            match_type = self.opts["event_match_type"]
salt/utils/event.py:618:            Default is opts['event_match_type'] or 'startswith'
salt/config/__init__.py:438:        "event_match_type": str,
salt/config/__init__.py:1225:        "event_match_type": "startswith",
salt/config/__init__.py:1469:        "event_match_type": "startswith",      "event_match_type": "startswith",

Potentially related results come from grep -nr "match_type"

Start with salt/utils/event.py, especially the event_match_type references, and compare the defaults in salt/config/init.py. Update doc/ref/configuration/master.rst and doc/ref/configuration/minion.rst to explain how the option is used and what startswith, endswith, find, regex, and fnmatch mean; done means both configuration references are documented.