fix (full-sync): Adding pino logger for probot update

[dolan-a]

With the Probot v14 update, it seems that logging in full-sync no longer works:

$ node --env-file=.env full-sync.js                               
Fatal error during full sync: TypeError: Cannot read properties of null (reading 'info')
    at performFullSync (/home/dol/dev/personal/safe-settings/full-sync.js:7:14)
    at Object.<anonymous> (/home/dol/dev/personal/safe-settings/full-sync.js:25:1)
    at Module._compile (node:internal/modules/cjs/loader:1761:14)
    at Object..js (node:internal/modules/cjs/loader:1893:10)
    at Module.load (node:internal/modules/cjs/loader:1481:32)
    at Module._load (node:internal/modules/cjs/loader:1300:12)
    at TracingChannel.traceSync (node:diagnostics_channel:328:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:245:24)
    at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5)
    at node:internal/main/run_main_module:33:47

This PR has the following changes:

1. Adds a logger (via already-installed pino)
2. Adds a few unit tests to confirm performFullSync in full-sync runs okay (test fails without the logger change; passes with it)