Feat: email recommendation for new speaker + date on deploy and webhooks

[HugoGresse]

• move the infos on the static API up UI Note for integration #158
• recommend the user when adding a new speaker to add his email, closing Require speaker email when adding manually a speaker #132
• save webhooks last trigger date, display it and also display the last event updated at on the update website button, close Add last answer date on webhook trigger  #54

[github-actions]

Visit the preview URL for this PR (updated for commit 15a2af5):

• https://conferencecenterr--pr191-email-speaker-reco-qctlfurk.web.app
• https://apiopenplanner--pr191-email-speaker-reco-ettprlc5.web.app

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