chore: adds broader .gitignore and packaging.yaml

[telpirion]

This PR adds two new files:

• A root-level .gitignore to help us keep the repo clean
• A packaging.yaml file to surface these samples on DAC

[gemini-code-assist]

Code Review

This pull request introduces a root .gitignore file with standard Android and IntelliJ exclusions, along with a .google/packaging.yaml file for sample metadata. The review feedback suggests enhancing the .gitignore by adding .kotlin/ for build consistency and secrets.properties to prevent accidental exposure of sensitive API keys. Additionally, it was noted that several IntelliJ-specific file entries are redundant as they are already covered by the .idea/ directory exclusion.

[gemini-code-assist]

The .kotlin/ directory is used for caching by the Kotlin compiler and scripts. It is already ignored in several sub-directory .gitignore files within this repository (e.g., AdaptiveJetStream/.gitignore). Adding it to the root .gitignore ensures consistent behavior across the project.

.gradle/
.kotlin/

[gemini-code-assist]

It is a security best practice to ignore secrets.properties, as it is commonly used by the Google Secrets Gradle plugin to store sensitive API keys. Including it in the root .gitignore helps prevent accidental commits of sensitive information.

local.properties
secrets.properties

[gemini-code-assist]

The entries misc.xml, deploymentTargetDropDown.xml, and render.experimental.xml are IntelliJ-specific configuration files that are typically stored within the .idea/ directory. Since .idea/ is already being ignored on line 21, these individual entries are redundant and can be removed to keep the .gitignore clean.

.idea/