Literal attribute rendered in deployment instructions for the downstream PostgreSQL connector

In Step 1.iii of 3.6.1. Deploying Debezium PostgreSQL connectors, an attempt was made to render the text in the code block in boldface to indicate that it represents user input.

However, the code block attributes of [subs="+macros,+attributes"] are not working as intended with the result that the value in the FROM line shows the attribute name that represents the base image path, rather then rendering the attribute value.

Removing the bolding and the `macros` attribute seems to fix the problem. Because the code block renders with a dark background and because the use of bold to designate user input is inconsistent, this is a relatively low-impact fix.

This change must be made in the upstream source, but it affects the downstream product documentation only.