Remove misleading table definitions

What does this MR do?

Problem

In the documentation for our markdown tables, the table definitions have misleading tables that - for example - increase the amount of hyphens for each subsequent column. In the cells, the text content also gets longer in each subsequent cell. Some users may infer that the cells are wider because of the increasing amount of hyphens, rather than that it's being computed dynamically from the content of the table body.

Fix

This MR updates the docs with three changes:

1. Each table example has exactly 3 hyphens
2. Duplicated table example columns with more than 3 hyphens are deleted entirely
3. The descriptive text of the table definition is updated to clearly state that 1 hyphen is all that's necessary, and controlling the width of the columns isn't possible.

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team