Add support for configuring default CookieSerializer using SessionCookieConfig

[vpavic]

This resolves #87.

The proposed solution doesn't map two attributes from SessionCookieConfig:

• secure: DefaultCookieSerializer#useSecureCookie defaults to null and relies on ServletRequest#isSecure which means mapping a value from SessionCookieConfig would override our default (since secure is a primitive boolean over there and typically defaults to false)
• httpOnly: DefaultCookieSerializer#useHttpOnlyCookie defaults to true in Servlet 3.0+ environments which means our default would be overridden in httpOnly typically defaults to false

Other than that integration tests in Boot based samples needed to be updated with explicit MockServletContext due to MockSessionCookieConfig#maxAge defaulting to 0 instead of -1. I've opened SPR-15142 to address that.

[vpavic]

PR updated due to SPR-15142 being fixed in the master via spring-projects/spring-framework#1298.