Add functions to SHOW TAG KEYS and SHOW FIELD KEYS

[tuykroa]

Then supported these 2 new functions : SHOW TAG KEYS & SHOW FIELD KEYS like InfluxDB show field keys in query-language https://docs.influxdata.com/influxdb/v1.7/query_language/schema_exploration/#show-field-keys

[x]Controlled

If you accept my contribution to this feature

[tuykroa]

Then supported these 2 new functions : SHOW TAG KEYS & SHOW FIELD KEYS like InfluxDB show field keys in query-language https://docs.influxdata.com/influxdb/v1.7/query_language/schema_exploration/#show-field-keys

[x]Controlled [x]Verified If you accept my contribution to this feature

[sebito91]

Thanks for the commit @tuykroa, really appreciate your help! If you're still interested in merging this PR can I please ask you to do the following:

• [ ] flush out the show tag keys command similar to what the documentation calls for, including capability to drill down on specific db or measurement
• [ ] flush out the show field keys command similar to the above
• [ ] add tests for show tag keys
• [ ] add tests for show field keys

You can use https://github.com/influxdata/influxdb-python/blob/8a8b8ff3c7d517959146c9daeb09c982a9c184b1/influxdb/client.py#L649 as an example.

Thanks!

[sebito91]

@tuykroa just following up to see if you were able to make some progress here?

[one4many]

I'm depending on this ... when does it get reviewed?