fix: Add S3 environment variables and fix REDIS_HOST bug

[btwshivam]

1. Fix REDIS_HOST bug in configmap_env.yaml - was incorrectly using

.Values.externalValkey.port instead of .Values.externalValkey.host

2. Add S3/AWS configuration support:

• Add AWS_BUCKET, AWS_DEFAULT_REGION, AWS_USE_PATH_STYLE_ENDPOINT to configmap
• Create secret_s3.yaml for S3 credentials (url, endpoint, access_key_id, secret_access_key)
• Add S3 secret references in deployment.yaml for AWS_URL, AWS_ENDPOINT,
  AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY

3. Support for existingSecret with S3 credentials

Fixes the missing S3 environment variables that prevented Pixelfed from
connecting to S3-compatible storage backends like SeaweedFS, MinIO, etc."

4. Fixed contact mail

• Changed {{- with .Values.pixelfed.instance.contact_email }} to {{- if .Values.pixelfed.instance.contact_email }}

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PR sponsored by Obmondo.com

Note: Since this is a company-paid contribution, we fork to the company account repo on GitHub. GitHub does not support "allow maintainer to edit in repo" for organization accounts.

• Maintainers can either provide feedback for required changes before merging, OR
• Pull our branch, make changes in their repo, and create a new PR including our commits.