[ADD] support for EsaLink

[remi-filament]

Hi @alexis-via I asked for an account on EsaLink in order to test both your library and module l10n_fr_einvoicing with another PA.

Thanks for you work, most of API is working without a change.

I have added support for EsaLink PA in your library with this PR.

There are a few divergences :

• SuperPDP added /afnor-flow/ or /afnor-directory/ in their URLs (probably to distinguish with their internal API routes, which Esalink did not add. So I added a configuration Entry on SuperPDP config : add_afnor_type_uri which I used in a function called _get_platform_base_url(session, type) which factors the retrieval of base_url which is called in most of functions
• EsaLink added a firewall in front of their API which you have to bypass using a specific header key : hubtimize-api-key which I added in config with a key name "extra-header-expected" and I add to session so that it is reused everywhere the oauth2 session is used.
• SuperPDP uses sortingOrder in directory-line/search sorting parameter when AFNOR API specifies that "order" should be used, so I added a configuration parameter on SuperPDP sorting_key to use this parameter instead of default "order"
• AFNOR API in PDF makes reference to totalNumberOfResults (used by SuperPDP) when annex specifies total_number_results (used by EsaLink) so I tweaked the code to support both

I also renamed plateform to platform everywhere.