Add generic specification for the Eclipse provisioning platform (p2)

In short, a p2 unit can be described via:
p2/<id>@<version>?classifier=...&location=...

PURL-TYPES.rst

@@ -397,6 +397,58 @@ nuget
 
       pkg:nuget/[email protected]
 
+p2
+----
+``p2`` for Eclipse p2 artifact:
+
+- A p2 artifact represents a piece of software that can be consumed using the
+  Eclipse Provisioning Platform. An artifact can represent various types of
+  components, such as Eclipse features, plug-ins or other bundles.
+
+- A p2 artifact is uniquely described by its id, version and classifier. A
+  namespace is therefore not necessary.
+
+- The name of the package url corresponds to the unique identifier of a given p2
+  artifact. This id uniquely identifies an artifact within the Eclipse
+  Provisioning Platform. 
+  Examples::
+
+      org.eclipse.core.resources.win32.x86_64
+      org.eclipse.rcp.sdk.id.executable.win32.win32.x86_64
+      org.eclipse.sdk
+
+- The version of the package url corresponds to the version of the p2 unit. The
+  version is required to distinguish between different releases of the same
+  artifact.
+  Examples::
+
+      3.5.500.v20220812-1420
+      2.0.0.202304281106
+
+- The `location` qualifier is an percent-encoded URI describing the physical
+  location of an artifact. This can for example be a repository accessed via
+  HTTPS, its Maven coordinates or an absolute file path to a local build result.
+  This qualifier is mandatory, because there is no central authority for hosting
+  p2 artifacts.
+  Examples::
+
+       https://download.eclipse.org/releases/2023-09
+       mvn:org.eclipse.platform:org.eclipse.core.runtime:3.29.0:jar
+
+- The `classifier` qualifier describes the type of artifact. This qualifier is
+  optional, with no default value.
+  Examples::
+
+        binary
+        org.eclipse.update.feature
+        osgi.bundle
+
+- Combined, those components then uniquely identify a p2 artifact. In short, the
+  format should be of the form p2/<id>@<version>?classifier=...&location=...
+  Examples::
+
+      pkg:p2/[email protected]?classifier=osgi.bundle&location=https%3A%2F%2Fdownload.eclipse.org%2Freleases%2F2023-09
+
 qpkg
 ----
 ``qpkg`` for QNX packages:
@@ -558,7 +610,6 @@ Other candidate types to define:
 - ``opam`` for OCaml packages:
 - ``openwrt`` for OpenWRT packages:
 - ``osgi`` for OSGi bundle packages:
-- ``p2`` for Eclipse p2 packages:
 - ``pear`` for Pear PHP packages:
 - ``pecl`` for PECL PHP packages:
 - ``perl6`` for Perl 6 module packages: