Update the doc of Impala components

We need to update some discription in the doc of Impala components.
https://impala.apache.org/docs/build/asf-site-html/topics/impala_components.html

In the section ofThe Impala Catalog Service, this is stale:

When you create a table, load data, and so on through Hive, you do need to issue REFRESH or INVALIDATE METADATA on an Impala daemon before executing a query there.

We should mention "Automatic Invalidation/Refresh of Metadata", a.k.a. HMS event processor, and add links for it.

Change "Impala daemons" to "Impala Coordinators" in this sentence:

The Impala component known as the Catalog Service relays the metadata changes from Impala SQL statements to all the Impala daemons in a cluster.

Also add this link for "On-demand Metadata"
https://impala.apache.org/docs/build/asf-site-html/topics/impala_metadata.html