docs: use ".. code-block:: shell-session" wherever relevant

The ".. code-block::" directive defined by Sphinx is more flexible, and
we have tried to enforce its use over ".. code::" for some time.
Similarly, the "bash" language passed as an argument to that directive
is often incorrect, as it should be used for bash scripts. For commands
to type in the console, "shell-session" should be preferred.

In this commit:

- Replace ".. code::" with ".. code-block::" everywhere.

- Replace "bash" with "shell-session" everywhere relevant (most of the
  occurrences).

- Fix the use of "::" (literal block, for raw output) versus the
  "code-block" directive (for code snippets). However, I have not
  checked all existing occurrences of ".. code-block::".

- Fix the use of the "parsed-literal" directive, which should be used
  only when there are RST elements to parse in the block (typically some
  RST substitutions).

- Fix a small number of minor formatting issues met when updating the
  directives.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>

Documentation/api.rst

@@ -37,7 +37,7 @@ can be pointed to an arbitrary API address.
 Example
 -------
 
-.. code:: bash
+.. code-block:: shell-session
 
     $ cilium -H unix:///var/run/cilium/cilium.sock
     [...]
@@ -61,7 +61,7 @@ Example
 
 The full example can be found in the `cilium/client-example`_ repository.
 
-.. code:: go
+.. code-block:: go
 
     import (
             "fmt"