Add the graylog2-es-timestamp-fixup tool.

(cherry picked from commit 1c9740e761174a6a21232a1d0ad0abd4ac4567c5)
Add tags to the built docker images.

(cherry picked from commit 6e70300c67b7f66bbcd3f0e7751000e9dde90b3f)
Bump to 0.91.1.
Update checksums due to new release artifacts.