Add a maintainers directive (#35083)

fixes #34879

This commit adds a new maintainer directive,
which by default extend the list of maintainers
for a given package.

The directive is backward compatible with the current
practice of having a "maintainers" list declared at
the class level.

lib/spack/docs/features.rst

@@ -116,7 +116,7 @@ creates a simple python file:
 
        # FIXME: Add a list of GitHub accounts to
        # notify when the package is updated.
-       # maintainers = ["github_user1", "github_user2"]
+       # maintainers("github_user1", "github_user2")
 
        version("0.8.13", sha256="591a9b4ec81c1f2042a97aa60564e0cb79d041c52faa7416acb38bc95bd2c76d")
 

lib/spack/docs/packaging_guide.rst

@@ -268,7 +268,7 @@ generates a boilerplate template for your package, and opens up the new
 
        # FIXME: Add a list of GitHub accounts to
        # notify when the package is updated.
-       # maintainers = ["github_user1", "github_user2"]
+       # maintainers("github_user1", "github_user2")
 
        version("6.2.1", sha256="eae9326beb4158c386e39a356818031bd28f3124cf915f8c5b1dc4c7a36b4d7c")
 
@@ -319,14 +319,8 @@ The rest of the tasks you need to do are as follows:
 
 #. Add a comma-separated list of maintainers.
 
-   The ``maintainers`` field is a list of GitHub accounts of people
-   who want to be notified any time the package is modified. When a
-   pull request is submitted that updates the package, these people
-   will be requested to review the PR. This is useful for developers
-   who maintain a Spack package for their own software, as well as
-   users who rely on a piece of software and want to ensure that the
-   package doesn't break. It also gives users a list of people to
-   contact for help when someone reports a build error with the package.
+   Add a list of Github accounts of people who want to be notified
+   any time the package is modified. See :ref:`package_maintainers`.
 
 #. Add ``depends_on()`` calls for the package's dependencies.
 
@@ -497,6 +491,31 @@ some examples:
 In general, you won't have to remember this naming convention because
 :ref:`cmd-spack-create` and :ref:`cmd-spack-edit` handle the details for you.
 
+.. _package_maintainers:
+
+-----------
+Maintainers
+-----------
+
+Each package in Spack may have one or more maintainers, i.e. one or more
+GitHub accounts of people who want to be notified any time the package is
+modified.
+
+When a pull request is submitted that updates the package, these people will
+be requested to review the PR. This is useful for developers who maintain a
+Spack package for their own software, as well as users who rely on a piece of
+software and want to ensure that the package doesn't break. It also gives users
+a list of people to contact for help when someone reports a build error with
+the package.
+
+To add maintainers to a package, simply declare them with the ``maintainers`` directive:
+
+.. code-block:: python
+
+   maintainers("user1", "user2")
+
+The list of maintainers is additive, and includes all the accounts eventually declared in base classes.
+
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