See merge request nexedi/slapos!1284

Probably I made a mistake when getting adding this md5sum in
70070a61 . This is not a case where the
checksum changed, we did not have checksum before anyway

See merge request !1282

to support git 2.38.1

This is a big changes for users, now typing "python" on the command line
will use system python if it exists or fail with "command not found".

`python3` is set to the SlapOS python from Theia software release.
Recommended approach for python users is either to get used to type
`python3` or to create a virtualenv and use it. With the virtualenv,
they can also install pylint or other linters, so this might be the
best thing to do.

This solves two problems:

First problem is that it makes the embedded SlapOS always have a python
interpreter as `python` in $PATH, which is not always the case in other
SlapOS usage and can hide problems that would cause a software to build
successfully in Theia but not in "bare metal" SlapOS.

Second problem problem is that on python was a interpreter from pygolang
and it is not perfect regarding line edition at least on python 3.8, as
we can observe in this session:

run python and type "something":

```
Python 3.8.13 (default, Sep  6 2022, 10:45:07)
[GCC 8.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> something
             ^ cursor is here, as expected
```

type Ctrl+A to go to beginning of line:

```
Python 3.8.13 (default, Sep  6 2022, 10:45:07)
[GCC 8.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> something
    ^ expected cursor position
^ actual cursor position
```

likewise, type Ctrl+E to go to end of line:

```
Python 3.8.13 (default, Sep  6 2022, 10:45:07)
[GCC 8.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> something
             ^ expected cursor position
         ^ actual cursor position
```

In some cases, for example when the instance does not have internet
access, or to speed up slapos node instance, it's better not to have
frontend requests in the embedded slapos. In this case, the default
slapos proxy behavior of returning a "fake frontend" [1] will apply
and promises checking frontend status will pass anyway.

[1]: see slapos.core commit 2a53efca2 (proxy: bypass simple fronten
requests by returning URL, 2019-03-25)

bring fixes for about 20 CVE

slapos.cookbook:haproxy no longer exist

See merge request nexedi/slapos!1278

Put broken python interpreters in path so that fail if they try to use
system python

We should not use $PYTHON, because this implicitly depends on the
python version that was used when the shared part is installed, leading
to this kind of problematic scenarios:
 - install the part from a python2.7 software, this creates scripts
  with "python2.7" in shebang line
 - install a python3 software referencing glib, it uses the shared
  part that was installed with python2, but "python2.7" is not in $PATH

By referencing the part explicitly, it becomes part of the signature
of the part, so a software on python2 and a software on python3 will
use a different version of the shared part.

945a2e97 (proxysql: bundled libinjection needs Python 2, 2021-12-23)
addressed the problem that proxysql was using system python, by placing
slapos' python in $PATH, but it added it after default $PATH, which
made proxysql use system python if available and only fallback to
slapos' python.
This changes the order of $PATH entries to always use slapos' python

python or python2 is system python, which we want to avoid

with support for aborting query ( https://github.com/mroonga/mroonga/issues/344 )

Configuring failover URL and being able to rely on cached content is not so
simple, thus document the requirement and prove in test, that such
configuration works correctly.