Update downstream docs in regards to deprecated elements

In Debezium 1.6, we deprecated several things:

• "MonitoredTables" metrics (snapshot and streaming metrics); replaced by "CapturedTables" metrics
• MySQL connector option "database.history.store.only.monitored.tables.ddl"; replaced by "database.history.store.only.captured.tables.ddl"

The following changes should be done to upstream docs:

• Un-document "database.history.store.only.monitored.tables.ddl" (users shouldn't be pointed to that legacy option any longer) <== Currently marked as deprecated upstream and down.
• Un-document the "adaptive" value for the "time.precision.mode" option (unrelated, but I just noticed it) <== Still appears upstream and downstream. See my comment from 21 Jan 2022.
• Un-document the "gtid.new.channel.position" option (unrelated, but I just noticed it) <== Conditionalized for upstream only and marked as deprecated, but still visible in the mySQL community docs.

The following changes should be done to downstream docs:

• Show database.history.store.only.monitored.tables.ddl with a deprecation notice (should be the case already) DONE.
• Add a deprecation notice to the MonitoredTables snapshot and streaming metrics DONE.
• The "gtid.new.channel.position" option is not shown in downstream docs, so no change needed (they were deprecated before moving to 1.0 GA)
• The adaptive value for time.precision.mode, still appears upstream and downstream for all SQL-based connectors except the MySQL connector. I forget ... is that correct? Previously, I thought that this had been removed downstream. See my comment below.