[E2E Test] Add E2E test for webserver release updates

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Description
Add a E2E test that does the following:

Runs a SLS state file that:

Installs nginx
Configures nginx to run a test website that returns Release 1.0 was successful in the body
Starts the nginx service

Here's the files for the nginx setup:

/srv/salt/nginx.sls

{% set root_path = "/usr/share/nginx/html/" %}

install_nginx:
  pkg.installed:
    - name: nginx

nginx_conf:
  file.managed:
    - name: /etc/nginx/nginx.conf
    - source: salt://files/nginx.conf
    - template: jinja
    - defaults:
        root_path: {{ root_path }};

nginx_website:
  file.managed:
    - name: {{ root_path }}index.html
    - makedirs: True
    - source: salt://files/index.html

start_nginx:
  service.running:
    - name: nginx
    - reload: True
    - enable: True
    - watch:
      - file: nginx_conf
      - file: nginx_website

nginx file (/srv/salt/files/nginx.conf):

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log notice;
pid /run/nginx.pid;
# Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.

include /usr/share/nginx/modules/*.conf;
events {
    worker_connections 1024;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';
    access_log  /var/log/nginx/access.log  main;
    sendfile            on;
    tcp_nopush          on;
    keepalive_timeout   65;
    types_hash_max_size 4096;
    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;
    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        listen       80;
        listen       [::]:80;
        server_name  _;
        root         {{ root_path }}
        # Load configuration files for the default server block.                                                                                                                     
        include /etc/nginx/default.d/*.conf;
        error_page 404 /404.html;
        location = /404.html {
        }
        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    }
}

index.html contents (/srv/salt/files/index.html)

<!doctype html>
<html>
  <head>
    <title>Version 1.0 of website</title>
  </head>
  <body>
    <p>Release 1.0 was successful</p>
  </body>
</html>

Run the state again and verify it does not have any changes
Verify in the test:

You can query the website and it contains the contents: Release 1.0 was successful

Now we need to update the test website and the nginx conf's root dir and update it with Salt.

update root directive in nginx config
update the body contents to Release 2.0 was successful
Run the state now and ensure the changes we expect occur in the state run.

Verify that the new content is updated: Release 2.0 was successful

Start by locating the repository's existing E2E test entry points, then use the described /srv/salt/nginx.sls, /srv/salt/files/nginx.conf, and /srv/salt/files/index.html setup as the test fixture. Run the state twice to check idempotence, query the website for the Release 1.0 text, update the root and page contents, and verify the second run applies the expected changes and serves Release 2.0.

Written by the indexing model from the issue text.

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