Ubuntu Core install hook plug

> The install hook runs in confinement. Access to this file needs to be granted via a system files interface and the right plug definition for the hook (`hooks.install.plugs`). But keep in mind that manual connection is only possible after installing a snap, which is too late. The install hook of a locally built and unsigned snap on a classic Ubuntu **cannot** be granted the access before the install hook's execution. This could work on classic Ubuntu if there is an auto connection assertion for the snap, when installed from the store.
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> On Ubuntu Core, the connection can be established before the installation, via the `connections` definition of the Gadget snap. Another alternative is via dedicated store auto connection assertions.

_Originally posted by @farshidtz in https://github.com/canonical/lora-basicstation-snap/pull/1#discussion_r1721749840_

Start by reviewing the install hook and the `hooks.install.plugs` definition, then compare Ubuntu Core's Gadget snap `connections` path with installation on classic Ubuntu. Confirm whether the requested pre-install access mechanism is available for a locally built and unsigned snap; done means the hook can receive the required file access before it runs.

Written by the indexing model from the issue text.