[docs] [infra] hugo shortcode updates

[polarweasel]

Problem: external-pointing links in admonitions (note, tip, warning) weren't getting styled correctly. This fixes that, and applies the same fix to several other shortcodes that turned out to have the same problem.

The updates allow external URLs (meaning any link that starts with http or https) to get styled as such, with the usual icon and a target of _blank. To test, have a look at the Cloud Troubleshooting page, at the bottom, and verify that the link to Yugabyte Support shows as external now. Or, have a look at the first note on the ddl_alter_table reference page, and verify that the link is styled correctly.

As for the grammar and syntax diagrams, the includeMarkdown shortcode has changed. So if they're still rendering correctly, that change passes the test. This PR also includes output from the latest version of the RRDiagram tool, which adds the ebnf language to the grammar code blocks, so those are syntax-highlighted now.

As a random example, please also verify that the code blocks and diagrams work on this page or another like it:

@netlify /latest/api/ysql/exprs/aggregate_functions/invocation-syntax-semantics/

[netlify]

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[bllewell]

This page has no notes, tips, or warnings. So what is there to check. The syntax diagrams seem to have come out OK. But why suspect that they would not?

[polarweasel]

@bllewell I've updated the link in the note that started this whole thing when you pointed out that links in notes weren't getting styled correctly.

Have a look at the first note on the ddl_alter_table reference page, and notice that the link (which is in markdown format as of commit 02d7ee4) is styled correctly.

As for the syntax diagrams, the includeMarkdown shortcode has changed. So if they're still rendering correctly, that change passes the test. 👍

[ddhodge]

LGTM

[lizayugabyte]

LGTM

[aishwarya24]

LGTM