Use common naming scheme for RST snippet files

[yoonspark]

Summary

RST snippets are used to reduce repetition of the same messaging (e.g., call to action for Slack's #support channel). Use common naming convention for these files.

Changes

• [x] Update file name and extension for the RST snippets

Testing

Locally verified that the documentation builds successfully. Pure docs update, so no other test needed.

Tickets

NA

[lionsardesai]

closing as not urgent. what we have works just fine.