Making sidecar to fill krb5.conf from parameters, passing DOMAIN in secret, general fixes and cleanup

[denispar]

Description of changes:

1. Fixed Dockerfile, if had a syntax error
2. Cleanup unused imports
3. Added separate sleep time for failure retries (not 45 minutes)
4. Fixed docstring for get_secret
5. get_secret now tries to get DOMAIN_NAME from the secret along with username and password
6. get_secret now doesn't crash everything if the secret is somehow misconfigured. Now we log and retry, the customer can fix the secret and we will pick it up on the next run.
7. The placeholders in krb5.conf are not populated from the code according to the parameters, no need to rebuild the container to change DOMAIN_NAME.
8. Fixed reading environment variables. os.environ values are always type str, not int as the old code assumed.

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[smhmhmd]

I do have some concerns/questions, pls do not merge yet