Specify which events were involved when logging that we are waiting for both GW and external sky maps

The only RAVEN-related log message describing why a coincidence was not that published that does not specify which events were involved is when both sky maps aren't available yet. We should add the events so the message goes from the following:

RAVEN: Will only publish GRB coincidence if spatial-temporal FAR is present. Waiting for both sky maps to be available first.

to in the future look like:

RAVEN: Will only publish GRB coincidence for S250108ha-E54307 if spatial-temporal FAR is present. Waiting for both sky maps to be available first.

See the following code: https://git.ligo.org/emfollow/gwcelery/-/blob/b92c14d8f30fc553650759c53910ec529ae35e69/gwcelery/tasks/raven.py#L598

changed milestone to %GWCelery 2.6.1 release

added External Triggers Logging Sky Maps labels

added to epic &12

I am assuming that this MR would go into GWCelery 2.6.1 release as pointed out by the Milestone. Adding a new section in the Changes.rst file for this new release.

assigned to @gaurav.waratkar

created branch 908-specify-which-events-were-involved-when-logging-that-we-are-waiting-for-both-gw-and-external to address this issue

mentioned in merge request !1574 (merged)

closed with merge request !1574 (merged)

Fixed by !1574 (merged)