SAMZA-2406: Add ConfigLoader interface and default PropertiesConfigLo…

[kw2542]

Add ConfigLoader interface and default PropertiesConfigLoader implementation, which will be used on AM to fetch configs.

The existing ConfigFactory interface will be deprecated and removed as we will not fetch configs on start up script run-app.sh anymore.

Design:
https://cwiki.apache.org/confluence/display/SAMZA/SEP-23%3A+Simplify+Job+Runner

Changes:

1. Add ConfigLoader interface which will be used in job coordinator to retrieve config from.
2. Add PropertiesConfigLoader which is a default implementation of ConfigLoader that reads a local properties file given the file path.

API Changes:
N/A. This is part of a series PRs, detailed information will be provided in the last/main PR.
Upgrade Instructions:
N/A. This is part of a series PRs, detailed information will be provided in the last/main PR.
Usage Instructions:
N/A. This is part of a series PRs, detailed information will be provided in the last/main PR.

Tests:

1. Add TestPropertiesConfigLoader to unit test PropertiesConfigLoader.

[prateekm]

@bharathkk and @abhishekshivanna offered to look at this.

@kw2542 Can you update usage/upgrade instructions in the description with changes required for using this new feature? This information will be collected for the release notes and changelog for the next release.

Let's also fix the commit title (wrapping).

[mynameborat]

Can we add more descriptive java docs?

1. It will be helpful if you can talk about how and when this interface is used.
2. What if ConfigLoader implementors want to handle dependency injection? Do we need to provide a factory for the config loader implementors?

[kw2542]

Added more descriptions.

[mynameborat]

I think a default constructor with config is too restrictive and violates separation of concerns, if we were to evolve ConfigLoader. ConfigLoader should not have to deal with dependency object construction and use. I'd prefer a factory that manages dependency injection for ConfigLoader so that its evolution doesn't affect the framework as long as the contract is maintained.

[mynameborat]

@bharathkk and @abhishekshivanna offered to look at this.

@kw2542 Can you update usage/upgrade instructions in the description with changes required for using this new feature? This information will be collected for the release notes and changelog for the next release.

Let's also fix the commit title (wrapping).

@kw2542 Can you also update the API changes in the description and add more details about this API (internal vs external) etc

[abhishekshivanna]

@kw2542 , could you also clarify as part of this patch the reason we need this new implementation over the existing config-factory (eg: PropertiesConfigFactory) and config-path implementation ? Is this meant to be a replacement for the way we do config loading today ? If so, should we deprecate the old way ?

[kw2542]

@kw2542 , could you also clarify as part of this patch the reason we need this new implementation over the existing config-factory (eg: PropertiesConfigFactory) and config-path implementation ? Is this meant to be a replacement for the way we do config loading today ? If so, should we deprecate the old way ?

[kw2542]

@kw2542 , could you also clarify as part of this patch the reason we need this new implementation over the existing config-factory (eg: PropertiesConfigFactory) and config-path implementation ? Is this meant to be a replacement for the way we do config loading today ? If so, should we deprecate the old way ?

Updated both the PR description as well as SEP itself.

ConfigLoader will replace ConfigFactory interface, which will be deleted in the following PRs.

[kw2542]

Discard to start a new PR clean.