docs: EXPOSED-684 Add documentation for exec() and move transaction docs to new element

[bog-walk]

Description

Summary of the change: Documentation about transactions now has its own top-level element with existing documentation as subtopics along with a new subtopic on working with SQL strings via exec().

Detailed description:

• Why:

There have been issues/questions in the past about the proper way to use exec() and the only documentation mentioning it is currently in the FAQ page.

There is a lot of information crammed into the single Transactions.md, which most likely deserves to be split and fleshed out into subtopics. Since the concept of a transaction is huge, and intertwines with other Exposed topics like exec(), Statements, and interceptors, it most likely needs its own section.

• How:
  • Remove FAQ section on how to use sql strings
  • Move original Transactions.md file and place it under a new top-level element 'Transactions'
  • Extract subsection on StatementInterceptors from Transactions.md to its own md file
  • Add new Working-with-SQL-Strings.md file that covers exec() information
  • Create new snippets project exposed-transactions that currently only has new code examples for new topic

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Type of Change

Please mark the relevant options with an "X":

• Documentation update

Checklist

• The build is green (including the Detekt check)
• Documentation for my change is up to date

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Related Issues

EXPOSED-684

[vnikolova]

Looks great 👍