Volunteer @SoloJacobs as release shepherd for v0.30 (#4736)

* retrofit RELEASE.md

It seems the `v0.29` was not documented. While this information is not
super accurate, it is the best I can find. This is the basis:
#4586

We can use this information to more easily plan the `v0.30` release.

Signed-off-by: Solomon Jacobs <[email protected]>

* Volunteer @SoloJacobs as release shepherd for v0.30

Signed-off-by: Solomon Jacobs <[email protected]>

---------

Signed-off-by: Solomon Jacobs <[email protected]>

Author: SoloJacobs

RELEASE.md

@@ -10,6 +10,8 @@ Release cadence of first pre-releases being cut is 12 weeks.
 | v0.26          | 2023-08-23            | Josh Abreu (Github: @gotjosh) |
 | v0.27          | 2024-02-28            | Josh Abreu (Github: @gotjosh) |
 | v0.28          | 2024-05-28            | Josh Abreu (Github: @gotjosh) |
+| v0.29          | 2024-10-09            | Joe Adams (Github: @sysadmind) |
+| v0.30          | 2025-12-12            | Solomon Jacobs (Github: @SoloJacobs) |
 
 If you are interested in volunteering please create a pull request against the [prometheus/alertmanager](https://github.com/prometheus/alertmanager) repository and propose yourself for the release of your choice.