Add 'front option to projectile-current-project-on-switch

[jtamagnan]

Foreword

I originally created #1879 but have since deleted that GitHub account,
as such the associated repository and pull request were closed.

This PR reopens that previous PR. #1895 on the other hand implements
Solution 2 of this pull request which I prefer.

Problem

There are certain modes for which the
projectile-find-file-hook-function function does not run by
default. This includes, shell, eshell, and magit. If one
navigates directly to one of these buffers and calls
projectile-relevant-known-projects while
projectile-current-project-on-switch is set to 'keep they will
notice that the first repository in the list is not the one that they
expect

Solution

There are two possible solutions that come immediately to mind. I
want to mention both of them for consideration though naturally
this PR only implements one of them:

1. Add a new 'front option for
   projectile-current-project-on-switch such that the first item is
   the project associated with the current buffer.
2. Modify projectile-mode to add the hook to
   buffer-list-update-hook such that the current buffer is always
   added to the list of known-projects.

This PR implements solution one as was done in #1879.
#1895 implements Solution 2

Comparision

The main drawback with Solution 1 is that the newly selected project
will not be added to the projects list.

The main drawback of Solution 2 is that it will not work on versions
of emacs earlier than 28.1 because of how buffer-list-update-hook
behaves on those older versions.

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