fix: set install_name to absolute path for libpact_ffi.dylib (#345)

[stan-is-hate]

Addresses #345
Tested by running the install command with and without --libDir.
Verified that my project's pact test compile and run correctly after installing libpact_ffi.dylib via a freshly built pact-go.
Verified otool output matches full path.
E.g.

~/github/pact-go install-name-tool ≡
15:05:16 🐠 
build/pact-go -l DEBUG install --libDir /tmp/
2023/10/02 15:05:18 [INFO] set lib dir target to /tmp/
2023/10/02 15:05:18 [INFO] package libpact_ffi not found
2023/10/02 15:05:18 [INFO] downloading library from https://github.com/pact-foundation/pact-reference/releases/download/libpact_ffi-v0.4.5/libpact_ffi-osx-x86_64.dylib.gz to /tmp/libpact_ffi.dylib
&{}
2023/10/02 15:05:19 [DEBUG] obtaining hash for file /tmp/libpact_ffi.dylib
2023/10/02 15:05:19 [DEBUG] writing config {map[libpact_ffi:{libpact_ffi 0.4.5 5971854e21bf8b41db8b821a77caa268}]}
2023/10/02 15:05:19 [DEBUG] writing yaml config to file libraries:
  libpact_ffi:
    libname: libpact_ffi
    version: 0.4.5
    hash: 5971854e21bf8b41db8b821a77caa268

2023/10/02 15:05:19 [INFO] setting install_name on library libpact_ffi for osx
2023/10/02 15:05:19 [DEBUG] running command: /usr/bin/install_name_tool -id /tmp/libpact_ffi.dylib /tmp/libpact_ffi.dylib
2023/10/02 15:05:20 [DEBUG] output from command []
2023/10/02 15:05:20 [INFO] package libpact_ffi found
2023/10/02 15:05:20 [INFO] checking version 0.4.5 of libpact_ffi against semver constraint >= 0.4.0, < 1.0.0
2023/10/02 15:05:20 [DEBUG] 0.4.5 satisfies constraints 0.4.5 >= 0.4.0, < 1.0.0
2023/10/02 15:05:20 [INFO] package libpact_ffi is correctly installed
2023/10/02 15:05:20 [DEBUG] skip checking ffi version() call because FFI not loaded. This is expected when running the 'pact-go' command.

~/github/pact-go install-name-tool ≡
15:05:23 🐠 
otool -D /tmp/libpact_ffi.dylib
/tmp/libpact_ffi.dylib:
/tmp/libpact_ffi.dylib

[mefellows]

Thanks for this, it looks OK to me and also works for me locally. If the build passes, I'll merge and release.

[YOU54F]

FYI golanglint-ci build failures & test failures addressed in the first commit of #351 but tangled in adding CI testing for other platforms which I haven't got passing x-plat yet. They are related to some modules not being supported after dropping go 1.17

[mefellows]

Thanks Saf. I'll see what I can do to address #312 and related PRs this morning.