Document that the SQLite version included in Ubuntu LTS, aside from ESM-only versions, is included in our support policy. (#19823)

The reason for querying this support was wanting support for SQLite's JSON operators, which are currently not present in the SQLite version found in Ubuntu's oldest supported LTS.

The JSON operators were used in some of the sticky events work (related: #19452).

Our ruling was that we should support Ubuntu oldest LTS equally to Debian oldstable, so support the oldest of the two versions from those.

That makes some kind of sense as it would be difficult to do otherwise without dropping support for that version of Ubuntu altogether, given if we kept publishing packages intended for use with Postgres, there's a risk that an innocent sysadmin would update their SQLite deployment without realising that it is no longer supported.

This was [discussed months ago
(private)](https://docs.google.com/document/d/12RZKPk3a4__JUSH9wYHODo9rRyKzsHg6BSCAcmqmbOU/edit?tab=t.0#bookmark=id.fcdvoc88dy5s)
and at [private](https://docs.google.com/document/d/12RZKPk3a4__JUSH9wYHODo9rRyKzsHg6BSCAcmqmbOU/edit?tab=t.0#bookmark=id.u48ivjge4qpt).

---------

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>

changelog.d/19823.doc

@@ -0,0 +1 @@
+Document that the SQLite version included in Ubuntu LTS, aside from ESM-only versions, is included in our support policy.

docs/deprecation_policy.md

@@ -22,7 +22,7 @@ people building from source should ensure they can fetch recent versions of Rust
 
 The oldest supported version of SQLite is the version
 [provided](https://packages.debian.org/oldstable/libsqlite3-0) by
-[Debian oldstable](https://wiki.debian.org/DebianOldStable).
+[Debian oldstable](https://wiki.debian.org/DebianOldStable) or the oldest maintenance/security-supported [Ubuntu LTS](https://endoflife.date/ubuntu) (Ubuntu versions with only Expanded Security Maintenance are not included).
 
 
 ### Context