fix: added custom dumper for pm4ml merge function

[vijayg10]

In custom_config/pm4ml-vars.yaml, if we pass the following values

core_connector_config:
  enabled: true
  env:
    TEST1_ID: '0720'
    TEST1_PREFIX: '00002893'
The value '0720' is passing to the generated helm values file correctly but the value '00002893' is being transformed as an integer without preceding zeros like 2893

Solution:
Added a custom dumper that works with yaml.dump function
Some explanation about this issue is here
yaml/pyyaml#98 (comment)
A leading zero in YAML 1.1 indicates an octal number, which can only have digits 0-7

[sijo5722-2021]

lgtm