Add integration test script

What does this MR do?

This MR moves existing CI tests to a script that can be used locally for faster iterations as well as adds new tests (TLS for example):

./spec/scripts/integration.sh

Screenshots or screen recordings

Click to see a failure example

❯ ./spec/scripts/integration.sh
Installation:
> Uninstall helm release if exists ...                      [OK]
> Helm install ...                                          [OK]
Healthchecks:
> Local | Legacy indexer health ...                         [OK]
> Local | New indexer health ...                            [OK]
> Local | Webserver health ...                              [OK]
> Internal Gateway | Legacy indexer health ...              [OK]
> Internal Gateway | New indexer health ...                 [OK]
> Internal Gateway | Webserver health ...                   [OK]
> External Gateway | Nginx health ...                       [OK]
Indexing & Searching:
> Local | Indexer truncate ...                              [OK]
> Local | Legacy indexer ...                                [OK]
> Local | Webserver ...                                     [OK]
> Local | Indexer ...                                       [OK]
> Internal Gateway | Legacy indexer indexing ...            [OK]
> Internal Gateway | Webserver ...                          [OK]
> External Gateway | Indexer ...                            [OK]
> External Gateway | Webserver ...                          [OK]
> External Gateway /nodes endpoint | Webserver search ...   [OK]
> External Gateway /nodes endpoint | Indexer ...            [OK]
TLS:
> Install cert manager ...                                  [OK]
> Add certificate ...                                       [OK]
> Enable TLS ...                                            [OK]
> TLS | External Gateway | Webserver ...                    [OK]
> TLS | External Gateway | Indexer ...                      [OK]
> TLS | External Gateway /nodes endpoint | Webserver ...    [FAIL]
 </html>nter>nginx</center>uest was sent to HTTPS port</center></title></head>ver, zoekt-indexer, zoekt-webserver, zoekt-gateway HTTP/1.1 400 Bad Request
Exit code: 1. Failed command: `kubectl exec gitlab-zoekt-0 -- curl -s -XPOST -d '{"Q":"prepare-commit-msg"}' 'https://gitlab-zoekt-gateway:8080/nodes/gitlab-zoekt-0.gitlab-zoekt.default.svc.cluster.local/api/search' -i -k | tee /dev/stderr | grep 'LineStart'`
Aborting the execution