Making Postgres.app relocatable

Currently, Postgres.app shows a warning and refuses to launch from a location other than /Applications

This is a frequent complaint from users, eg.:

As a first step towards making Postgres.app relocatable was to use relative links for shared libraries, which we completed a year ago:

Making Postgres.app relocatable causes a lot of potential issues, because then people could end up using multiple copies of Postgres.app simultaneously (on purpose or by accident). We've tried to document how we expect Postgres.app to behave on this Wiki page: https://github.com/PostgresApp/PostgresApp/wiki/Requirements-for-making-Postgres.app-relocatable

The next steps towards making Postgres.app relocatable are the following:

Postgres.app should show binary path in server info #692
User should be able to bypass /Applications check (implemented in 78d9ad8)
Absolute paths in the GUI app should be replaced with relative paths (implemented in 561a2d8)
LoginHelper and MenuHelper should work from locations other than /Applications

Use relative paths for PostgreSQL binaries instead of hardcoding /App…

Postgres.app should detect when it is translocated (either by launching from disk image or in certain other circumstances) and do the following:

New behavior when translocated

don't install login item
don't launch menu helper
disable menu checkbox in prefs
disable "automatically launch postgres on login" checkbox (pre-ventura)
add label to preferences "Postgres.app is currently translocated. Please move it to a permanent location to use all features. [More Info]"
stop all servers with binaries inside the translocated app when quitting GUI

Feature was finished in commit 3c62eae.

Will be released in next update.

Released in Postgres.app 2.6.7