Add caching support for REST Attribute Aggregator

[Jong-Vincent]

Hi all,

We've made the following additions to the REST aggregator:

• It is possible to define a cache endpoint. Cache data is retrieved based on a configurable cron schedule, this data will be used if an exception occurs during the initial retrieval of data. Using the cache is disabled by default to stay backwards compatible.
• It is possible to set whether an empty value should be used if a desired attribute cannot be mapped. By default, no attributes are added if nothing can be mapped to stay backwards compatible.

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (4636902) 92.39% compared to head (8d7d8b5) 93.25%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #48 +/- ## ============================================ + Coverage 92.39% 93.25% +0.86% - Complexity 376 419 +43 ============================================ Files 66 69 +3 Lines 986 1068 +82 Branches 59 69 +10 ============================================ + Hits 911 996 +85 + Misses 53 46 -7 - Partials 22 26 +4 ``` | [Files](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext) | Coverage Δ | | |---|---|---| | [...va/aa/aggregators/AbstractAttributeAggregator.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvYWdncmVnYXRvcnMvQWJzdHJhY3RBdHRyaWJ1dGVBZ2dyZWdhdG9yLmphdmE=) | `82.85% <100.00%> (+0.50%)` | :arrow_up: | | [...r/src/main/java/aa/config/TaskSchedulerConfig.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvY29uZmlnL1Rhc2tTY2hlZHVsZXJDb25maWcuamF2YQ==) | `100.00% <100.00%> (ø)` | | | [...java/aa/model/AttributeAuthorityConfiguration.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvbW9kZWwvQXR0cmlidXRlQXV0aG9yaXR5Q29uZmlndXJhdGlvbi5qYXZh) | `96.55% <100.00%> (+0.25%)` | :arrow_up: | | [aa-server/src/main/java/aa/model/Cache.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvbW9kZWwvQ2FjaGUuamF2YQ==) | `100.00% <100.00%> (ø)` | | | [.../aggregators/AttributeAggregatorConfiguration.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvYWdncmVnYXRvcnMvQXR0cmlidXRlQWdncmVnYXRvckNvbmZpZ3VyYXRpb24uamF2YQ==) | `81.57% <83.33%> (+5.10%)` | :arrow_up: | | [aa-server/src/main/java/aa/model/CacheFilter.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvbW9kZWwvQ2FjaGVGaWx0ZXIuamF2YQ==) | `83.33% <83.33%> (ø)` | | | [...a/aa/aggregators/rest/RestAttributeAggregator.java](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext#diff-YWEtc2VydmVyL3NyYy9tYWluL2phdmEvYWEvYWdncmVnYXRvcnMvcmVzdC9SZXN0QXR0cmlidXRlQWdncmVnYXRvci5qYXZh) | `96.77% <95.29%> (-1.82%)` | :arrow_down: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/OpenConext/OpenConext-attribute-aggregation/pull/48/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenConext)

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