feat: [UIF-1010] Add swiftype metatag for site of ksqldb

[mt206]

Description

https://confluentinc.atlassian.net/browse/UIF-1010

In order to support more sophisticated, faceted search in docs.confluent.io, we are looking at adding some meta tags to a number of websites that are currently included in docs' swiftype search engine. This will allow search results to be targeted at specific sites (and languages).

The following sites are involved:

Site	Id
https://docs.confluent.io/	1
https://www.confluent.io/blog/	2
https://developer.confluent.io/	3
https://docs.ksqldb.io/en/latest/	4
https://kafka-tutorials.confluent.io/	5
https://api.telemetry.confluent.cloud/docs	6

The change involved is minimal and would be to add the following meta tag into the main template file of each site:
<meta class="swiftype" name="site-id" data-type="integer" content="4" />

Please let me know if there is any issue that you foresee with this change or if you have any questions.

Additional reading: https://swiftype.com/documentation/site-search/guides/schema-design#crawler