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.

• [x] Have you adhered to the repository's defined coding convention rules?
• [x] Have you updated the 'documentation.md' file with the method/function documentation?
• [x] Have you sent a message along with the result or response?
• [x] Have you used the try-catch technique?
• [x] 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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