Fix regex error in Log4j-config.xsd

[MalKeshar]

Trivial fix of error "The value of the facet 'pattern' is not a valid regular expression"

Before:

$ xmllint --schema Log4j-config.xsd /tmp/log4j2.xml --noout
regexp error : failed to compile: Wrong escape sequence, misuse of character '\'
regexp error : failed to compile: internal: no atom generated
regexp error : failed to compile: generate transition: atom == NULL
regexp error : failed to compile: xmlFAParseAtom: expecting ')'
regexp error : failed to compile: xmlFAParseRegExp: extra characters
Log4j-config.xsd:131: element pattern: Schemas parser error : Element '{[http://www.w3.org/2001/XMLSchema}pattern':](http://www.w3.org/2001/XMLSchema%7Dpattern':) The value '(|disable|\$\{[^{}]+\})' of the facet 'pattern' is not a valid regular expression.
...

And few same messages

After:

$ xmllint --schema log4j-core/src/main/resources/Log4j-config.xsd /tmp/log4j2.xml --noout
/tmp/log4j2.xml validates

[vy]

@MalKeshar, thanks, much appreciated! The XSD misses a huge set of the available components and I am actively working on a project that will auto-generate this file from scratch. I expect to deliver a complete XSD within a couple of weeks. To avoid merge conflicts, and since there is a better solution in the making, I am inclined to close this PR. @ppkarwasz, thoughts?

[ppkarwasz]

I am closing this, since we'll remove the manually written schema soon.

I added a task pointing to this PR in the #1954 milestone. @MalKeshar, while the specific problem you are reporting will automatically cease to exist, when the file is deleted, we'll apply the procedure you suggested to the generated XSD file.