merged subject dropdown and add subject and made suggestion list with add subjects when not present

[PriyanshiAgrawal1345]

Description

I have merged the subject dropdown list functionality and added a new subject option in 1 functionality in which I made a combo box that will suggest the subjects already present in the server in the form of a dropdown and if the subject user enters is don't present in the server then add a new subject in server.
Additionally, I resolved the issue of landing on the login page while clicking the SignUp button.

Resolves: [8]

Checklist

Before submitting this pull request, kindly verify that the ensuing checkpoints have been reached.

• Have you adhered to the repository's defined coding convention rules?
• Have you updated the 'documentation.md' file with the method/function documentation?
• Have you sent a message along with the result or response?
• Have you used the try-catch technique?
• Has the method/class been added to the documentation (md file)?

Screenshots

Additional Notes/Comments

Any additional remarks or suggestions concerning this pull request are welcome.

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[github-actions]

Great job, @PriyanshiAgrawal1345! 🎉 Thank you for submitting your pull request. Your contribution is valuable and we appreciate your efforts to improve our project.

We will promptly review your changes and offer feedback. Keep up the excellent work! Kindly remember to check our contributing guidelines