Add support for folder-based MASTG-TEST

[cpholguera]

Currently, tests in tests-beta/ are structured like OWASP/mastg/tests-beta/**/**/MASTG-TEST-****.md.

We need to update this to OWASP/mastg/tests-beta/**/**/MASTG-TEST-****/MASTG-TEST-****.md similar to how our demos/ work. But still support OWASP/mastg/tests-beta/**/**/MASTG-TEST-****.md for backwards compatibility for now.

In addition to that, tests in the MASTG-TEST-****/ folders will support one or more testing methods.

Each method is a method-*.md file (e.g. method-1.md, method-2.md, etc.)

---
platform: android
type: static
---

Some intro...

## Steps

...

## Observation

...

The automation will inject any existing methods into the main MASTG-TEST-****.md file before the Evaluation section.

---
platform: android
title: References to APIs and Permissions for Accessing External Storage
id: MASTG-TEST-0202
...
type: [<<add unique list of types from methods>>]
---

## Overview

...

<<inject methods here>>

## Evaluation

...

Example:

ls OWASP/mastg/tests-beta/android/MASVS-STORAGE/MASTG-TEST-0202/
MASTG-TEST-0202.md
method-1.md
method-2.md
method-3.md
method-4.md

Would render as:

---
platform: android
title: References to APIs and Permissions for Accessing External Storage
id: MASTG-TEST-0202
...
type: [static]
---

## Overview

...

## Method 1 - Static Analysis

Some intro...

### Steps

...

### Observation

...

## Method 2 - Static Analysis

Some intro...

### Steps

...

### Observation

...

## Method 3 - Dynamic Analysis

Some intro...

### Steps

...

### Observation

...

## Method 4 - Network Analysis

Some intro...

### Steps

...

### Observation

...

## Evaluation

...