Updates to reflect 3.12 release and future plans

[ShyamsundarR]

• Updates the main page releases section
• Updates the release schedule page
• Updates the roadmap page
• Updates the downloads (install) page

Signed-off-by: ShyamsundarR srangana@redhat.com

[ShyamsundarR]

Please do not merge till 3.12 is released and packages are in place. This change is in preparation for the release.

We would also need to closely review the new release schedule for the future releases.

[amarts]

This is good to go now?

[ShyamsundarR]

This will be merged sometime today by @amye as we make the release announcement.