R1:1c32c9b965a5

Improve granluarity and defaults of `security.allow-outbound-http`

Summary:
Ref T6755. This is a partial fix, but:

- Allow netblocks to be blacklisted instead of making the feature all-or-nothing.
- Default to disallow requests to all reserved private/local/special IP blocks. This should generally be a "safe" setting.
- Explain the risks better.
- Improve the errors rasied by Macro when failing.
- Removed `security.allow-outbound-http`, as it is superseded by this setting and is somewhat…