Enable accessing Tomcat manager

[RodBruce]

I want to access the Tomcat manage webapp. When I click on the manager webapp link in the default Tomcat "It works!" page I get a 403 'Forbidden' error. I followed the documentation to set up access but I still would get the 403 error.

I finally figured out that the SynValve configuration in the file:
/etc/tomcat9/context.xml
prevents access to the Tomcat manager webapp.

I figured out that I could add a Valve to the manager context in the file:
/etc/tomcat9/Catalina/localhost/manager.xml
That would override the SynValve.

Here is what I wound up adding:

`

    <Valve className="org.apache.catalina.valves.RemoteAddrValve"
        allow="127\.\d+\.\d+\.\d+|::1|0:0:0:0:0:0:0:1|10\.\d+\.\d+\.\d+" />
    <Manager sessionAttributeValueClassNameFilter="java\.lang\.(?:Boolean|Integer|Long|Number|String)|org\.apache\.catalina\.filters\.CsrfPreventionFilter\$LruCache(?:\$1)?|java\.util\.(?:Linked)?HashMap"/>

`

Could we add a file that allows only access from localhost (similar to what Tomcat does by default) and then include in the documentation that this is where you go to configure access?