Rename / move telemetry documentation to "Product Analytics"

GitLab is renaming ~"group::telemetry" to ~group::product analytics

Rename telemetry-related documentation:

Titles
Names within the Telemetry guide

As shown here, this affects some directories within the gitlab repo tree; we'll need some redirection pages:
```
mike@worklaptop-mj:~$ ls dev/gitlab/doc/telemetry/
index.md  snowplow.md
mike@worklaptop-mj:~$ ls dev/gitlab/doc/development/telemetry/
event_dictionary.md  index.md  snowplow.md  usage_ping.md
```
- Example: we'd move content from doc/development/telemetry/index.md to doc/development/product_analytics/index.md, and then replace doc/development/telemetry/index.md with a redirect (similar to that in doc/telementry/index.md
Rename the titles in the left-nav bar, under Development; requires changes to default-nav.yml in the gitlab-docs repo.