Add Data-Layer Helpers to comet-common

[liyaka]

This pull request introduces a set of new Helm template helpers and schema definitions to standardize and simplify configuration for MySQL, Redis, and S3 across charts. It adds reusable helper templates for each service, updates the schema to support these new options, and bumps the chart version to reflect these enhancements.

New configuration helpers and schema support:

• MySQL helpers and schema:

  • Added templates/_mysql.tpl with a comprehensive set of helpers for MySQL connection, admin credentials, SSL, AWS/IAM, connection pooling, and replicated endpoints. Also includes connection URL builders for both primary and read-only connections.
  • Extended values.schema.json to define the new .Values.global.mysql object, documenting all supported MySQL configuration options, including replication and client certificate support.

• Redis helpers and schema:

  • Added templates/_redis.tpl with helpers for retrieving Redis configuration values and generating Redis URLs, supporting flexible parameterization (database selection, SSL, username/password, etc.).
  • Extended values.schema.json to define the new .Values.global.redis object, documenting supported Redis configuration options.

• S3 helpers and schema:

  • Added templates/_s3.tpl with helpers for S3 configuration value retrieval and region-aware S3 endpoint normalization.
  • Extended values.schema.json to define the new .Values.global.s3 object, documenting S3 and object storage configuration options.

General Helm improvements:

• Added a helper to return the proper image pull policy with a default of "IfNotPresent".
• Bumped chart version from 0.1.0 to 0.2.0 in Chart.yaml to reflect these changes.