✨(frontend) Teacher dashboard: implement contract sign process

[rlecellier]

Feature Request

:warning: This issus must follow https://github.com/openfun/richie/issues/2075

On teacher dashboard "page signatures" teacher must be able to:

• sign one contract (row action)
• sign multiple contract (table action)

To do so we will:

• request joanie to get LexPersona signature link for one or for multiple contract its. (see backend endpoint issus)
• open a modal that render LexPersona signature iframe (see "Create contract sign container" issus)
• refetch contracts on "page signature" when the modal is closed