'accessPolicy' is mis-represented and mis-understood

[StephenMolloy]

This pull request updates documentation for IIS handler attributes, specifically clarifying the behavior of requireAccess and accessPolicy attributes. It introduces additional explanatory notes to improve understanding of their functionality and execution context.

Updates to requireAccess attribute:

• Updated the description of requireAccess to emphasize its role in determining the execution level of a handler and added a note explaining that handlers may still be initialized even if their requireAccess value does not match the current accessPolicy level. (iis/configuration/system.webServer/handlers/add.md)

Updates to accessPolicy attribute:

• Enhanced the description of accessPolicy to clarify its purpose as a filtering mechanism rather than a strict security policy and added a note explaining its interaction with the requiredAccess attribute. (iis/configuration/system.webServer/handlers/index.md)

Additional updates:

There are docs in the older "unmaintained" trove of IIS documentation that reference this feature. I know there are great warnings about how we don't maintain those docs, but every so often someone sees a handler get initialized when it doesn't meet the requireAccess policy and gets confused and files an issue that comes back to a PG. I can't open a PR on those. Not sure if they should also be updated or if we really don't maintain them anymore.

• https://learn.microsoft.com/en-us/previous-versions/iis/settings-schema/ms689475(v=vs.90)
• https://learn.microsoft.com/en-us/previous-versions/iis/settings-schema/ms691481(v=vs.90)
• https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/hh831697(v=ws.11)

[wadepickett]

Looks great.