boost181: Install Boost CMake find scripts by default

[mvieth]

Description

CMake transitions more and more towards using Boost's BoostConfig.cmake, which is only installed if the option --no-cmake-config is not given. The documentation of the variant also mentions that these CMake scripts should be installed by default.
See also https://cmake.org/cmake/help/latest/module/FindBoost.html

Type(s)

• bugfix
• enhancement
• security fix

Tested on

Unfortunately, I have no macOS available to test this on. I would argue that, since I am effectively turning the variant on by default, the risk of this change is small.

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL in commit message?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[macportsbot]

Notifying maintainers:
@mascguy for port boost181.
@michaelld for port boost181.

[barracuda156]

This is indeed desirable, see: pika-org/pika#1236

[mvieth]

@mascguy @michaelld Friendly ping. Would be great if you could review this. Thanks in advance!

[mascguy]

Sorry for the delay, completely forgot about this PR. Thanks for the reminder, aa well as the contribution!

[mascguy]

P.s. Oh, you need to rev-bump the port too