[4.x.x] Make siddhi application core thread pool size configurable

[shadhini]

Make siddhi app core thread pool size configurable

When number of triggers per a siddhi application exceeds 6, triggers won't reinitialize after db re-connection due to hard corded core pool size of 5. https://github.com/wso2-support/siddhi/blob/8b1ace31c1d645d5a2fc47844a5a55ef6ddd282d/modules/siddhi-core/src/main/java/org/wso2/siddhi/core/util/parser/SiddhiAppParser.java#L162.

Thus, this PR makes siddhi application core thread pool size configurable.

Here, if the following config is added to the conf/worker/deployment.yaml file, the value given in the config as \ would be used as the core pool size. If not, default value of 5 would be used as the core pool size.

siddhi:
  properties:
    appThreadPoolSize: <APP_THREAD_POOL_SIZE>

e.g:

siddhi:
  properties:
    appThreadPoolSize: 10

Issue link: https://github.com/wso2-enterprise/financial-open-banking/issues/6933

Doc Issue:

Applicable Labels: siddhi-core-4.2.20

Related PRs:

• https://github.com/wso2-support/siddhi/pull/210
• https://github.com/wso2-support/siddhi/pull/211

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