[Sponsor] Add new sponsor

**About Sponsors:**
A Sponsor is a legal entity that sponsors a CSO’s activity (be it a project or a programme or the CSO itself) by giving it a specific amount of money the CSO needs to spend in a limited amount of time. A grant duration may vary, the most common grants are given for a 12 month period.
In the context of the current platform a Sponsor will be an entity that can have one or more contracts with the CSO. The relationship between sponsors and the CSO is one or many to one. The situation in which a project/programme is sponsored by more Sponsors is extremely rare and it is not covered in this version of ALEX.

**Feature description: A user can add a new Sponsor**

Flow:
1. Go to the sidebar menu left side of the screen > click on 'Adauga Sponsor' [to replace 'Finantatori' with 'Sponsori' in Figma] [Figma: add new sponsor ](https://www.figma.com/file/W7ppl5xGFpB3atVWwYL7qN/Alex-(asistentul-bugetar-al-ONG-urilor)?type=design&node-id=5065-65859&t=fdU8o1GOqHlVystJ-4)
2. a new form will open
3. User need to fill in details in each input fields:
- field 1: fill in 'Denumire sponsor' - [mandatory, input text field]
- field 2: fill in 'Alias' - [mandatory, input text field]
- field 3: fill in 'CUI/CIF' - [mandatory, input text field]
- field 4: fill in 'Nume și prenume' - [mandatory, input text field]
- field 5: fill in'Telefon' - [mandatory, input text, number]
- field 6: fill in'E-mail' - [mandatory, input text field, standard email validations: @, . ]
- field 7: fill in 'Adresa de corespondenta' - [mandatory, input text field]
- field 8: fill in'Observatii' - [optional, input text field]
4. User can save a sponsor
* when pressing it it will save the information into “Lista sponsori” and the sponsor status will be "inactiv" until the sponsor is assigned to a Grant;
* if a mandatory field is not completed and the user clicks on the _Save_ button, then the empty mandatory field will have a red border (as described in [Style](https://www.figma.com/file/W7ppl5xGFpB3atVWwYL7qN/Alex-(asistentul-bugetar-al-ONG-urilor)?type=design&node-id=4603-45446&mode=design&t=xuylP3WjlAZDx1wo-4))

Inizia dal flusso Figma collegato ed esamina i pattern API esistenti nel repository per entità comparabili. Il lavoro è completato quando gli utenti possono inviare i campi dello sponsor elencati con la validazione specificata, salvare lo sponsor nell’elenco degli sponsor e vederlo contrassegnato come inattivo finché non viene assegnato a un grant.

Scritto dal modello di indicizzazione a partire dal testo della issue.