add subscriptions sample

[jacalata]

A new sample program showing how to create a subscription.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tableauserverclient
__init__.py	7	0	100%
config.py	15	0	100%
datetime_helpers.py	25	1	1	96%
exponential_backoff.py	20	0	100%
filesys_helpers.py	31	0	100%
namespace.py	26	3	3	88%
tableauserverclient/bin
_version.py	358	212	212	41%
tableauserverclient/helpers
__init__.py	1	0	100%
headers.py	13	8	8	38%
logging.py	2	0	100%
strings.py	27	1	1	96%
tableauserverclient/models
__init__.py	41	0	100%
column_item.py	55	32	32	42%
connection_credentials.py	35	11	11	69%
connection_item.py	77	10	10	87%
custom_view_item.py	138	13	13	91%
data_acceleration_report_item.py	54	1	1	98%
data_alert_item.py	159	3	3	98%
data_freshness_policy_item.py	156	15	15	90%
database_item.py	207	36	36	83%
datasource_item.py	247	11	11	96%
dqw_item.py	104	5	5	95%
exceptions.py	4	0	100%
favorites_item.py	56	8	8	86%
fileupload_item.py	19	0	100%
flow_item.py	149	10	10	93%
flow_run_item.py	72	0	100%
group_item.py	81	3	3	96%
groupset_item.py	39	1	1	97%
interval_item.py	182	32	32	82%
job_item.py	188	10	10	95%
linked_tasks_item.py	80	1	1	99%
metric_item.py	130	12	12	91%
pagination_item.py	34	0	100%
permissions_item.py	110	12	12	89%
project_item.py	157	31	31	80%
property_decorators.py	100	18	18	82%
reference_item.py	23	1	1	96%
revision_item.py	60	0	100%
schedule_item.py	206	6	6	97%
server_info_item.py	37	4	4	89%
site_item.py	610	12	12	98%
subscription_item.py	103	3	3	97%
table_item.py	118	18	18	85%
tableau_auth.py	61	24	24	61%
tableau_types.py	25	1	1	96%
tag_item.py	15	0	100%
target.py	6	0	100%
task_item.py	57	2	2	96%
user_item.py	277	17	17	94%
view_item.py	179	15	15	92%
virtual_connection_item.py	64	8	8	88%
webhook_item.py	66	0	100%
workbook_item.py	289	16	16	94%
tableauserverclient/server
__init__.py	9	0	100%
exceptions.py	4	0	100%
filter.py	21	1	1	95%
pager.py	35	1	1	97%
query.py	143	15	15	90%
request_factory.py	1108	149	149	87%
request_options.py	261	2	2	99%
server.py	176	19	19	89%
sort.py	6	0	100%
tableauserverclient/server/endpoint
__init__.py	33	0	100%
auth_endpoint.py	78	12	12	85%
custom_views_endpoint.py	149	13	13	91%
data_acceleration_report_endpoint.py	21	0	100%
data_alert_endpoint.py	97	25	25	74%
databases_endpoint.py	110	30	30	73%
datasources_endpoint.py	320	37	37	88%
default_permissions_endpoint.py	47	5	5	89%
dqw_endpoint.py	43	16	16	63%
endpoint.py	181	20	20	89%
exceptions.py	70	6	6	91%
favorites_endpoint.py	95	22	22	77%
fileuploads_endpoint.py	51	0	100%
flow_runs_endpoint.py	65	11	11	83%
flow_task_endpoint.py	23	3	3	87%
flows_endpoint.py	216	58	58	73%
groups_endpoint.py	136	10	10	93%
groupsets_endpoint.py	74	8	8	89%
jobs_endpoint.py	71	12	12	83%
linked_tasks_endpoint.py	38	0	100%
metadata_endpoint.py	88	14	14	84%
metrics_endpoint.py	58	8	8	86%
permissions_endpoint.py	47	5	5	89%
projects_endpoint.py	153	26	26	83%
resource_tagger.py	135	43	43	68%
schedules_endpoint.py	100	11	11	89%
server_info_endpoint.py	36	10	10	72%
sites_endpoint.py	126	28	28	78%
subscriptions_endpoint.py	58	15	15	74%
tables_endpoint.py	108	36	36	67%
tasks_endpoint.py	65	7	7	89%
users_endpoint.py	130	16	16	88%
views_endpoint.py	142	10	10	93%
virtual_connections_endpoint.py	115	11	11	90%
webhooks_endpoint.py	57	11	11	81%
workbooks_endpoint.py	339	28	28	92%
TOTAL	10833	1381	87%

[bcantoni]

@jacalata this one has a lot of cruft in it - might be best to start over from the current dev branch and just add your new samples/subscriptions.py