[DOCS] Add documentation for other kibana.yml settings we have from security solutions

[FrankHassanabad]

Description

We have had a few settings added to kibana.yml in which I don't think developers communicated to documentation that they are there and should be documented.

We should document these settings for our users if we exposed them.

They are:

xpack.securitySolution.maxRuleImportExportSize
xpack.securitySolution.maxRuleImportPayloadBytes
xpack.securitySolution.maxTimelineImportExportSize
xpack.securitySolution.maxTimelineImportPayloadBytes

They each have these defaults if not set within kibana.yml of:

maxRuleImportExportSize: 10000,
maxRuleImportPayloadBytes: 10485760
maxTimelineImportExportSize: 10000
maxTimelineImportPayloadBytes: 10485760

A description of each is pretty much this (feel free to change wording):

maxRuleImportExportSize - The maximum number of rules you can import or export. If you exceed this number you cannot import or export without changing this value to a higher number.

maxRuleImportPayloadBytes - The maximum size in bytes of importing rules. If you exceed this in bytes you cannot import without reducing your number of import bytes or changing this value to a higher number.

maxTimelineImportExportSize - The maximum number of timelines you can import or export. If you exceed this number you cannot import or export without changing this value to a higher number.

Although I marked this as v7.14.0, these settings have existed since at least v7.8.0. No user has complained directly about needing these settings but I still think its best we document them since we maintain them and they exist but I'm fine with however far back these should go, including if they are only in v7.14.0

A linked PR which mentions these and moving them around with v7.8.0 marked on it:
elastic/kibana#63430