Allow overriding the installation directory

[joca-bt]

Allow overriding the installation directory when installing with the install.sh script. For example, via a script argument.

[YOU54F]

we could make this only set if unset with =?

pact-broker-cli/install.sh

Line 117 in bc25f0a

PACT_BROKER_CLI_BIN_PATH=${PWD}

allowing the user to specify via an environment variable

[joca-bt]

That would also work.