Make request body size limit configurable

Usage related changes

Close #408
Introduce a new CLI parameter: --request-body-size-limit <BYTES>
- Default: 2000000 (2 MB) - so far this was the only value used
- This is more flexible than implementing a boolean flag parameter

Refactor: extract host, port, timeout and request_body_size_limit to ServerConfig
Remove redundant code from ServerConfig

[x] Checked the relevant parts of development docs
[x] Applied formatting - ./scripts/format.sh
[x] No linter errors - ./scripts/clippy_check.sh
[x] No unused dependencies - ./scripts/check_unused_deps.sh
[x] Performed code self-review
[x] Rebased to the latest commit of the target branch (or merged it into my branch)
[x] Updated the docs if needed, including the TODO section
[x] Linked the issues which this PR resolves
[x] Updated the tests if needed; all passing (execution info)