chore: install pgbouncer from PGDG

[NiccoloFei]

PGDG allow us to install the latest versions earlier, given that newer versions transition later on to the debian repositories.

Also, I've simplified the update process to use the Renovate Deb datasource (and fixed an existing regexp that was not matching).

Closes #67

[NiccoloFei]

 "regex": [
   {
     "deps": [
       {
         "depName": "debian",
         "currentValue": "trixie-slim",
         "currentDigest": "sha256:1caf1c703c8f7e15dcf2e7769b35000c764e6f50e4d7401c355fb0248f3ddfdb",
         "datasource": "docker",
         "versioning": "loose",
         "replaceString": "// renovate: datasource=docker versioning=loose\nbase = \"debian:trixie-slim@sha256:1caf1c703c8f7e15dcf2e7769b35000c764e6f50e4d7401c355fb0248f3ddfdb\"",
         "updates": [
           {
             "updateType": "digest",
             "newValue": "trixie-slim",
             "newDigest": "sha256:18764e98673c3baf1a6f8d960b5b5a1ec69092049522abac4e24a7726425b016",
             "branchName": "renovate/debian-trixie-slim"
           }
         ],
         "packageName": "debian",
         "warnings": []
       }
     ],
     "matchStrings": [
       "\\/\\/\\s*renovate:\\s*datasource=(?<datasource>.*?)\\s+(versioning=(?<versioning>.*?))?\\s*[A-Za-z0-9_-]+\\s*=\\s*\"(?<depName>[^:]+):(?<currentValue>[^\\s@]+)(@(?<currentDigest>sha256:[0-9a-f]*))?\""
     ],
     "versioningTemplate": "{{#if versioning}}{{{versioning}}}{{else}}semver{{/if}}",
     "packageFile": "docker-bake.hcl"
   },
   {
     "deps": [
       {
         "depName": "pgbouncer",
         "currentValue": "1.24.1-1",
         "datasource": "deb",
         "registryUrls": [
           "https://download.postgresql.org/pub/repos/apt?suite=trixie-pgdg&components=main&binaryArch=amd64"
         ],
         "replaceString": "// renovate: suite=trixie-pgdg depName=pgbouncer\npgBouncerVersion = \"1.24.1-1\"",
         "updates": [
           {
             "bucket": "non-major",
             "newVersion": "1.25.0-1.pgdg13+1",
             "newValue": "1.25.0-1.pgdg13+1",
             "newMajor": 1,
             "newMinor": 25,
             "newPatch": 0,
             "updateType": "minor",
             "isBreaking": false,
             "branchName": "renovate/pgbouncer-1.x"
           }
         ],
         "packageName": "pgbouncer",
         "versioning": "deb",
         "warnings": [],
         "registryUrl": "https://download.postgresql.org/pub/repos/apt?suite=trixie-pgdg&components=main&binaryArch=amd64",
         "homepage": "https://www.pgbouncer.org/",
         "currentVersion": "1.24.1-1",
         "isSingleVersion": true,
         "fixedVersion": "1.24.1-1"
       }
     ],
     "matchStrings": [
       "\\/\\/\\s*renovate:\\s*?(suite=(?<suite>.*?))?\\s*depName=(?<depName>.*?)?\\s*[A-Za-z0-9_-]+\\s*=\\s*\"(?<currentValue>.*)\""
     ],
     "datasourceTemplate": "deb",
     "registryUrlTemplate": "https://download.postgresql.org/pub/repos/apt?suite={{#if suite}}{{suite}}{{else}}stable{{/if}}&components=main&binaryArch=amd64",
     "packageFile": "docker-bake.hcl"
   }
 ]
}

Pasting here the changes that would be done by renovate.