Add Central v2024.2 upgrade instructions

[lognaturel]

See #1855

[matthew-white]

Just wanted to check, is this PR ready for review / to be merged?

[lognaturel]

We'll want to add a link to https://github.com/getodk/docs/pull/1859/files#diff-d1fd5d1b68bb4a3d5db94b2138eaf7ab19c8f8eeee5d9c69a6745a58d5e6eed1R330

Maybe you could plan on doing that after #1859 is merged either by pushing a commit here or doing another PR?

[lognaturel]

I added the link because I realized I wanted to change some wording too. The build will be broken but I think we can squash and merge after #1859 and follow up if there are any issues on master.

[matthew-white]

Looks great. 👍 Exciting to read about these improvements!

[matthew-white]

Looking at the PR description and at edits to #1855, I'm realizing that you were probably using #1855 to prepare these docs. I actually intended that one to be the tracking issue for .3. I had a separate issue for .2 at #1786, but I moved some notes from #1786 to #1855 when it looked like they weren't going to be relevant to the .2 release. I just now moved some notes back from #1855 to #1786 (e.g., about S3). Sorry, my moving things around was probably a source of confusion. 😬 I don't think there's any issue, I just wanted to make a note of the two tracking issues.

One bullet that #1786 has that I think hasn't been captured yet is that users will no longer need to rebuild after configuring a custom cert. My understanding is that that's true of .2 even though it isn't just a change to .env, though maybe that's not right. But I think it makes sense to document that after this PR. I've copied the bullet to #1855 so we don't lose track of it.