upload: Enable File Upload for users.

[Subhasish-Behera]

What does this PR do, and why?

External discussion & connections

• [x] Discussed in #zulip-terminal in File Upload #T529 #T1414
• [x] Fully fixes #529
• [ ] Partially fixes issue #
• [ ] Builds upon previous unmerged work in PR #
• [ ] Is a follow-up to work in PR #
• [ ] Requires merge of PR #
• [ ] Merge will enable work on #

How did you test this?

• [ ] Manually - Behavioral changes
• [ ] Manually - Visual changes
• [ ] Adapting existing automated tests
• [ ] Adding automated tests for new behavior (or missing tests)
• [ ] Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• [ ] It is a minimal coherent idea
• [ ] It has a commit summary following the documented style (title & body)
• [ ] It has a commit summary describing the motivation and reasoning for the change
• [ ] It individually passes linting and tests
• [ ] It contains test additions for any new behavior
• [ ] It flows clearly from a previous branch commit, and/or prepares for the next commit

Visual changes

[neiljp]

I left feedback in the stream, so removing needs-review flag, unless there are specific concerns?

[zulipbot]

Heads up @Subhasish-Behera, we just merged some commits that conflict with the changes you made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.