Install available updates alongside installation of packages to remove known vulnerabilities from images.

Example for issues in plain alpine:3 image (v3.20):

```sh
$ grype alpine:3
 ✔ Vulnerability DB                [updated]
 ✔ Loaded image                                                            alpine:3
 ✔ Parsed image                    sha256:1d34ffeaf190be23d3de5a8de0a436676b758f48f
 ✔ Cataloged contents              dac15f325cac528994a5efe78787cd03bdd796979bda52fd
   ├── ✔ Packages                        [14 packages]
   ├── ✔ File digests                    [77 files]
   ├── ✔ File metadata                   [77 locations]
   └── ✔ Executables                     [17 executables]
 ✔ Scanned for vulnerabilities     [8 vulnerability matches]
   ├── by severity: 0 critical, 0 high, 6 medium, 0 low, 0 negligible (2 unknown)
   └── by status:   8 fixed, 0 not-fixed, 0 ignored
NAME           INSTALLED   FIXED-IN    TYPE  VULNERABILITY   SEVERITY
busybox        1.36.1-r28  1.36.1-r29  apk   CVE-2023-42365  Medium
busybox        1.36.1-r28  1.36.1-r29  apk   CVE-2023-42364  Medium
busybox-binsh  1.36.1-r28  1.36.1-r29  apk   CVE-2023-42365  Medium
busybox-binsh  1.36.1-r28  1.36.1-r29  apk   CVE-2023-42364  Medium
libcrypto3     3.3.0-r2    3.3.0-r3    apk   CVE-2024-4741   Unknown
libssl3        3.3.0-r2    3.3.0-r3    apk   CVE-2024-4741   Unknown
ssl_client     1.36.1-r28  1.36.1-r29  apk   CVE-2023-42365  Medium
ssl_client     1.36.1-r28  1.36.1-r29  apk   CVE-2023-42364  Medium
```

Issue would be solved by also upgrading installed packages:

```sh
$ apk -U upgrade --no-cache
fetch https://dl-cdn.alpinelinux.org/alpine/v3.20/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.20/community/x86_64/APKINDEX.tar.gz
(1/5) Upgrading busybox (1.36.1-r28 -> 1.36.1-r29)
Executing busybox-1.36.1-r29.post-upgrade
(2/5) Upgrading busybox-binsh (1.36.1-r28 -> 1.36.1-r29)
(3/5) Upgrading libcrypto3 (3.3.0-r2 -> 3.3.1-r0)
(4/5) Upgrading libssl3 (3.3.0-r2 -> 3.3.1-r0)
(5/5) Upgrading ssl_client (1.36.1-r28 -> 1.36.1-r29)
Executing busybox-1.36.1-r29.trigger
OK: 8 MiB in 14 packages
```

Furthermore, this commit reduces accidental complexity from the Docker build process.
Most notably, use pre-made official golang images for building postgres-operator.