Docs: Remove explicit release tag in Docker image name (#5671)

The documentation on running AiiDA in a Docker container was suggesting:

    docker pull aiidateam/aiida-core:|release|

Where `|release|` would be substituted with the current version of the
package that was being built. However, since the v2.0 release, we started
adding the `.post0` suffix to the version number in the `main` branch.
This means that the `latest` documentation branch, which builds directly
of the `main` branch would generate, for example, the instruction:

    docker pull aiidateam/aiida-core:2.0.4.post0

But this would of course fail as that version does not exist on Docker
hub. Instead, we can simply use the `latest` identifier:

    docker pull aiidateam/aiida-core:latest

Since the `latest` build of the documentation should reference the latest
code release, this should be normally be correct.

docs/source/intro/run_docker.rst

@@ -21,13 +21,13 @@ This image contains a fully pre-configured AiiDA environment which makes it part
 
       .. parsed-literal::
 
-         $ docker pull aiidateam/aiida-core:\ |release|\
+         $ docker pull aiidateam/aiida-core:latest
 
       Then start the container with:
 
       .. parsed-literal::
 
-         $ docker run -d --name aiida-container aiidateam/aiida-core:\ |release|\
+         $ docker run -d --name aiida-container aiidateam/aiida-core:latest
 
       You can use the following command to block until all services have started up:
 
@@ -88,7 +88,7 @@ This image contains a fully pre-configured AiiDA environment which makes it part
 
       .. parsed-literal::
 
-         $ docker run -d --name aiida-container --mount source=my-data,target=/tmp/my_data aiidateam/aiida-core:\ |release|\
+         $ docker run -d --name aiida-container --mount source=my-data,target=/tmp/my_data aiidateam/aiida-core:latest
 
       Starting the container with the above command, ensures that any data stored in the ``/tmp/my_data`` path within the container is stored in the ``my-data`` volume and therefore persists even if the container is removed.