docs: fix standalone compose examples' port bindings

[circa10a]

In the standalone compose examples, the ports aren't bound to the host so the instructions of telling a user to access via localhost aren't valid. I've updated the examples where a user can now access the UI as well as the http events collector (the events collector localhost POST request example didn't work either).

Using current instructions:

❯ curl -k https://localhost:8088/services/collector/event -H "Authorization: Splunk abcd1234" -d '{"event": "hello world"}'
curl: (7) Failed to connect to localhost port 8088: Connection refused

Using updated instructions:

❯ curl -k https://localhost:8088/services/collector/event -H "Authorization: Splunk abcd1234" -d '{"event": "hello world"}'
{"text":"Success","code":0}

[nwang92]

The failing image scan is due to CVE-2020-29363, which was addressed in #448 and should be fixed by #444.

I'll go ahead and merge this in - thanks for the contribution!