tools: update release notes template

The given template comes from the time, when we had 1.10 and 2.x with
the old release policy (see [1]). In fact, almost every aspect of this
template is obsolete now.

For example, we have no stable and non-stable releases anymore: there
are pre-releases (marked with alpha, beta, rc keywords) and releases. We
don't need to say explicitly that the given release is stable.

Also, 1.10 is not LTS anymore (it is EOL) and 2.11 is not the latest
series.

The links needs an update too.

So, I decided to write these templates from scratch, but keep the idea:
give some release status information, highlight notable changes (for
feature releases), provide a few hints about the update procedure.

[1]: https://github.com/orgs/tarantool/discussions/6182

NO_DOC=dev tools
NO_CHANGELOG=same
NO_TEST=same

Author: Totktonada

tools/gen-release-notes

@@ -51,84 +51,56 @@ BUGFIXES_ANCHOR = '{{BUGFIXES}}'
 OVERVIEW_TEMPLATE = """
 ## Overview
 
-// {{{ BETA X.Y.1
+// {{{ 3.x
 
-**TBD** is the [beta][release_policy] version of the **TBD** release series.
+Tarantool 3.x is the recommended release series. Users of Tarantool 2.11 are
+encouraged to update to the latest 3.x release.
 
-This release introduces {{FEATURES}} new features and resolves {{BUGFIXES}} bugs since
-the **TBD** version. There can be bugs in less common areas. If you find any,
-feel free to [report an issue][issues] on GitHub.
+This release introduces {{FEATURES}} improvements and resolves {{BUGFIXES}}
+bugs since **TBD**.
 
 Notable changes are:
 
 * **TBD**
 * **TBD**
 * **TBD**
 
-[release_policy]: https://www.tarantool.io/en/doc/latest/dev_guide/release_management/#release-policy
-[issues]: https://github.com/tarantool/tarantool/issues
+// }}} 3.x
 
-// }}} BETA X.Y.1
+// {{{ 2.11
 
-// {{{ STABLE X.Y.{2,3}
+2.x is the old stable release series. Users are encouraged to update to the
+latest 3.x release.
 
-**TBD** is the **TBD**th [stable][release_policy] version of the **TBD** release
-series. It introduces {{FEATURES}} improvements and resolves {{BUGFIXES}} bugs since
-**TBD**.
+This is a bugfix release. It resolves {{BUGFIXES}} issues since the previous
+version.
 
-The "stable" label means that we have all planned features implemented and we
-see no high-impact issues. However, if you encounter an issue, feel free to
-[report it][issues] on GitHub.
+// }}} 2.11
 
-[release_policy]: https://www.tarantool.io/en/doc/latest/dev_guide/release_management/#release-policy
-[issues]: https://github.com/tarantool/tarantool/issues
-
-// }}} STABLE X.Y.{2,3}
-
-// {{{ LTS 1.10.Z
-
-**TBD** is the next stable release in the [long-term support (LTS)
-version][release_policy][release_policy] 1.10.x release series.
-
-The label "stable" means there are 1.10.x-based applications running in
-production for quite a while without known crashes, incorrect results or
-other showstopper bugs.
-
-This release introduces {{FEATURES}} improvements and resolves roughly {{BUGFIXES}}
-issues since the **TBD** version.
-
-[release_policy]: https://www.tarantool.io/en/doc/1.10/dev_guide/release_management/#release-policy
-[issues]: https://github.com/tarantool/tarantool/issues
-
-// }}} LTS 1.10.Z
+Please, consider the full list of user-visible changes below.
 """.strip()  # noqa: E501 line too long
 
 COMPATIBILITY_TEMPLATE = """
 ## Compatibility
 
-// {{{ BETA / STABLE 2.Y.Z
-
-Tarantool 2.x is backward compatible with Tarantool 1.10.x in the binary data
-layout, client-server protocol, and replication protocol.
-
-Please [upgrade][upgrade] using the `box.schema.upgrade()` procedure to unlock
-all the new features of the 2.x series.
+Tarantool 2.x and 3.x are compatible in the binary data layout, client-server
+protocol, and replication protocol. It means that the updating may be performed
+with zero downtime for read requests and the-order-of-network-lag downtime for
+write requests.
 
-[upgrade]: https://www.tarantool.io/en/doc/latest/book/admin/upgrades/
-
-// }}} BETA / STABLE 2.Y.Z
+Please, follow the [upgrade procedure][upgrade] to plan your update actions.
 
-// {{{ LTS 1.10.Z
+// {{{ 3.x
 
-Tarantool 1.10.x is backward compatible with Tarantool 1.9.x in binary data
-layout, client-server protocol and replication protocol.
+Users of Tarantool 2.x may be interested in the [compat][compat] options that
+allow to imitate some 2.x behavior. This allows to perform application code
+update step-by-step, not all-at-once.
 
-Please [upgrade][upgrade] using the `box.schema.upgrade()` procedure to unlock
-all the new features of the 1.10.x series.
+[compat]: https://www.tarantool.io/en/doc/latest/reference/configuration/configuration_reference/#compat
 
-[upgrade]: https://www.tarantool.io/en/doc/1.10/book/admin/upgrades/
+// }}} 3.x
 
-// }}} LTS 1.10.Z
+[upgrade]: https://www.tarantool.io/en/doc/latest/book/admin/upgrades/
 """.strip()  # noqa: E501 line too long
 
 ENTERPRISE_TEMPLATE = """