stroom:format-date() documentation needs revamp

[DS177]

Using the format-date() function confusing for non-UK locations if following the Stroom Documentation examples.
TimeZone ID needs to be in long format eg Europe/London, Pacific/Auckland, Australia/Canberra. But this is not intuitive from the documentation provided.

Change documentation to be more helpful:

• Show working examples of all 5 arguments.
• Expected output of examples is always useful.
• Changing GMT/BST in the doco to be Europe/London
• Above 3 things would probably be OK but an example or two from other timezones would be useful
• Maybe something re timezone/offset format a bit like what is in [https://binkley.blogspot.com/2019/02/java-date-time-timezone-formats.html] . I'm not sure whether Stroom format-date() supports all these options so it would be good to know.

Also current documentation example 3 incorrect - 'GMT+1:00' should be 'GMT+0100'

In attached documents:
Tests 1-3 correspond to the first three examples in Stroom documentation format-date().
Tests 4-6 correspond to the Stroom unit tests.
Tests 7-12 is attempts to get it timezone working for NZ. Several issues here - The 'NZ' ID works for date/time but can't generate an offset if this is the ID. The 'NST' fails completely. I would have thought I should use NZST/NZDT for the 5th argument but that generates errors. Have to use 'Pacific/Auckland' as timezone to get things working OK

Additional info in Slack #stroom-content 15Nov21

[at055612]

This is the page in question

https://gchq.github.io/stroom-docs/docs/user-guide/pipelines/xslt/xslt-functions/#format-date

[at055612]

Loosely related to #78 in the sense that some of the docs need to be generated from java annotations in the code.