We have a track record of Time-Zone inconsistencies in the events of the
project website (e.g. opensearch-project#1616, opensearch-project#1805, opensearch-project#2288, opensearch-project#2418, opensearch-project#2422, opensearch-project#2431, opensearch-project#2449).

In order to detect these inconsistencies earlier, make the `tz`
mandatory and check that the Time-Zone offset match the Time-Zone name.
These checks require a working bundle so run it on GitHub actions and
keep the old pre-commit check to only check date formatting using basic
UNIX tooling.

Adjust the events templates to match what we expect.

While here, also check that non-online events have the needed
`location.city` and `location.country`.

Signed-off-by: Romain Tartière <[email protected]>

Most of these events have a Time-Zone offset of -0700 or -0800 which makes
me think they are all using the America/Los_Angeles Time-Zone (sometimes
with the wrong offset, which will be fixed in another commit).

Updated with:
```
grep -r --files-without-match '^tz:' _events | xargs sed -i '' -E -e'/^online:/a\
tz: America/Los_Angeles'
```

Signed-off-by: Romain Tartière <[email protected]>

These inconsistencies are now being reported, when -0700 and -0800 are
used incorectly.

Signed-off-by: Romain Tartière <[email protected]>

According to the meetup page, the event was on 24.01.2023 at 19:00 local
time.  The Time-Zone offset then correspond to Europe/Warsaw.

Signed-off-by: Romain Tartière <[email protected]>

The website says it started on the 25th and not the 24th in
Charlottesville, same Time-Zone as New York (America/Charlottesville not
being a valid Time-Zone name).

Signed-off-by: Romain Tartière <[email protected]>

These one have the correct offset, but when adding `tz` we did not took
this into account.

Use the America/New_York offset which match the events.

Signed-off-by: Romain Tartière <[email protected]>

These are not RFC822 time representations.  So do not call them that
name, it just add confusion.

Signed-off-by: Romain Tartière <[email protected]>

Signed-off-by: Romain Tartière <[email protected]>