Fixed missing slash for user avatar

[HUisHU-Christian]

ISSUE NAME

When sending an email to the users, the avatar cannot be resolved in case it is in a subfolder (app.base is set).

This pull request is a (multiple allowed):

• [x] bug fix
• [ ] change of existing behavior
• [ ] new feature

What you did

Grep for 'img/avatar/user.png' revealed that usually a slash is written before. This might be necessary as the subdirectory in the config/passbolt.php file defaults without a slash. In the long run, there should be a check for it (like: if slash missing -> add slash)

This said, it might make sense to rewrite this PR to something even bigger.

[CLAassistant]

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[cedricalfonsi]

Thank you very much for your contribution. @pabloelcolombiano will review your PR and come back to you, reference: PB-21497

[ishanvyas22]

Hey @HUisHU-Christian, we've applied this fix see https://github.com/passbolt/passbolt_api/commit/c65d010ce0fa0757176946b679f7080d253c848d & https://github.com/passbolt/passbolt_api/commit/f2d341c1544b5da710f95d979a9693058d4936ca. This has also been published with the v3.9.0 release.

Thank you for your contribution ❤️