feat(mailer): add ejs template handling

src/app.module.ts

src/configuration/config.ts

src/configuration/configuration.service.ts

src/mailer/mail-templates/changeEmail.ejs

src/mailer/mail-templates/changeEmail.json

src/mailer/mail-templates/verify.ejs

src/mailer/mail-templates/verify.json

src/mailer/mailer.module.ts

src/mailer/mailer.service.spec.ts

src/mailer/mailer.service.ts

src/structures/structures.module.ts

template.env