Allow multi-line code snippets in Markdown tables

[adutra]

This change enhances the chart.valueDefaultColumnRenderMd template which now uses multi-line code snippets with <pre> tags.

The default values are rendered with a new template: chart.valueDefaultColumnRenderInline. Any line breaks are replaced with <br/> since Markdown table cells cannot have line breaks.

HTML is properly escaped when default values are surrounded by backticks, e.g. `<span>foo</span>` is rendered as <pre>&lt;span&gt;foo&lt;/span&gt;</pre>, but <span>foo</span> is rendered as <pre><span>foo</span></pre> without escaping. This behavior matches the existing behavior for Markdown tables.

The "tpl" notation type is also supported.

The motivation for this change is that Markdown tables are generally better rendered by websites like Hugo than HTML tables, but single-line snippets often make the "Default" column too wide and the overall table layout becomes unbalanced.

[norwoodj]

Gotta resolve your merge conflicts

[adutra]

Gotta resolve your merge conflicts

Fixed, sorry about that.

[adutra]

FYI there might be a small regression for people doing custom values with Markdown markup. For example:

# -- The foo value.
# @default -- Default is `bar` or `qix`.
foo: ~

Now this would have to be changed to:

# -- The foo value.
# @default -- Default is <code>bar</code> or <code>qix</code>.
foo: ~

[adutra]

@norwoodj would you have some time soon to have a look? Thanks! 🙏