Deps: Add wordpress lint dependency (2.0.0) to aztec module

Release Notes: https://github.com/wordpress-mobile/
WordPress-Lint-Android/releases/tag/2.0.0

Since the 'aztec' module is still using Java files in it, it makes
sense to utilize the 'org.wordpress:lint' library on it. All other
modules are all Kotlin, with no Java files in it. As such, there is no
point in utilizing the 'org.wordpress:lint' library on any other module.

FYI: As of version '2.0.0' has only one rule, which informs about
missing null annotation on Java classes.

aztec/build.gradle

@@ -72,6 +72,8 @@ dependencies {
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$kotlinCoroutinesVersion"
 
     implementation 'org.apache.commons:commons-lang3:3.8.1'
+
+    lintChecks "org.wordpress:lint:$wordpressLintVersion"
 }
 
 project.afterEvaluate {

build.gradle

@@ -69,6 +69,7 @@ ext {
 }
 
 ext {
+    // mixed
     gradlePluginVersion = '3.3.1'
     kotlinCoroutinesVersion = '1.6.4'
     tagSoupVersion = '1.2.1'
@@ -80,5 +81,9 @@ ext {
     wordpressUtilsVersion = '3.5.0'
     espressoVersion = '3.0.1'
 
+    // other
+    wordpressLintVersion = '2.0.0'
+
+    // project
     aztecProjectDependency = project.hasProperty("aztecVersion") ? "org.wordpress:aztec:${project.getProperty("aztecVersion")}" : project(":aztec")
 }