feat: add email registration function

[luhaoling]

🔍 What type of PR is this?

This PR is added to support email registration.

👀 What this PR does / why we need it:

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

🅰 Which issue(s) this PR fixes:

#222

📝 Special notes for your reviewer:

When you want to use other maibox to send email,you just to update the fileds "sendMail senderAuthorizationCode smtpAddr smtpPort" of the config/config.yaml.

🎯 Describe how to verify it

When you invoke the send verification api, fill in the email and leave the mobile number field blank.

📑 Additional documentation e.g., RFC, notion, Google docs, usage docs, etc.:

None.

[kubbot]

CLA Assistant Lite bot: 💕 Thank you for your contribution and please kindly read and sign our 🎯https://github.com/openim-sigs/cla/blob/main/README.md.
If you wish to sign the CRA, Please copy and comment on the following sentence:

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request}

[cubxxw]

You need to specify an issue

[luhaoling]

You need to specify an issue

OK,I understand.

[luhaoling]

I have read the CLA Document and I hereby sign the CLA

[luhaoling]

You need to specify an issue

I hava specified an issue.