Redpanda currently supports only virtual-hosted style URLs
for use with S3.

Add `s3_url_style` to `cloud_storage_clients/types.h" to allow for
future work towards supporting path-style URLs.

To support path-style requests in addition to the currently supported
virtual-host style, 's3_url_style' has been added to 's3_configuration',
as well as 'request_creator'.

New methods 'make_host()' and 'make_target()' in 'request_creator'
will generate host and target strings according to the url style set
for 's3_client' requests (currently defaulted to virtual-host).

Allow user to set s3_url_style in their redpanda configuration
file. New setting 'cloud_storage_url_style' can be set to
'virtual_host' or 'path'.

Added the option for `url_style` to `s3_test_client_main.cc`,
allowing for testing of both virtual-style and path-style requests.

Also make sure the `url_style` is initialized correctly everywhere
the `s3_configuration` object is created.

The addressing style used by `redpanda` for ducktape tests can now
be set with the variable `cloud_storage_url_style` in `SISettings`,
or injected into a test similar to `cloud_storage_type` with a decorator.

e.g: `@matrix(cloud_storage_url_style=['path','virtual_host'])`