Meta: Enable CodeQL static analysis for Serenity

CodeQL is a static analysis technology that was purchased by GitHub
and has been tightly integrated into the platform. It's different
from most other static analysis solutions because it's based on a
database built from your codebase, and then language specific rules
can be executed against that database. The rules are fully user
extensible, and are written in a datalog/query language.

The default cpp language rules coming from CodeQL will probably find
some issues, the ability to easily write custom rules/queries will
lend it self nicely to allowing us to validate Serenity specific
semantics are followed throughout the code.

References:
- https://www.youtube.com/watch?v=AMzGorD28Ks
- https://securitylab.github.com/tools/codeql

.github/codeql/config.yml

@@ -0,0 +1,8 @@
+name: "SerenityOS CodeQL Config"
+
+queries:
+ - uses: security-and-quality
+ - uses: security-extended 
+
+# Documentation for configuring CodeQL is located here:
+# https://docs.github.com/en/free-pro-team@latest/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning