Fix const-correctness for pointer variables to referred strings

[kraj]

Mark pointer variables 'e' as 'const char *' in
config_parse_netlog_remote_address,file_in_same_dir, and socket_address_parse, since they point to memory they do not own or modify.

Summary

Brief description of the changes.

Fixes #(issue number)

Changes

Testing

• meson test -C build passes
• Tested with UDP/TCP/TLS as applicable
• New code has test coverage (if applicable)

Checklist

• Code follows systemd coding style
• Commit messages are clear and descriptive
• Documentation updated (if applicable)
• No new compiler warnings

[ssahani]

We do not do sign Off. Please drop that.

Also

git commit --amend -m "fix: constify pointer variables referring to strings

Ensure const-correctness by updating char* to const char* where strings are not modified.
Prevents accidental mutation of string literals and improves safety."