Add rich_text_input block element support

[seratch]

This pull request adds a few changes for supporting rich_text_input block element on modals and Home tabs:

• Add rich_text_input block element to slack-api-model and slack-api-model-kotlin-extension
• Add rich_text_value patterns (view_submission and block_actions) to slack-app-backend library

references:

• https://api.slack.com/reference/block-kit/block-elements#rich_text_input

Category (place an x in each of the [ ])

• [ ] bolt (Bolt for Java)
• [ ] bolt-{sub modules} (Bolt for Java - optional modules)
• [ ] slack-api-client (Slack API Clients)
• [x] slack-api-model (Slack API Data Models)
• [x] *slack-api--kotlin-extension** (Kotlin Extensions for Slack API Clients)
• [x] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[codecov[bot]]

Codecov Report

Merging #1215 (890550d) into main (ab7374c) will decrease coverage by 0.05%. The diff coverage is 57.69%.

@@             Coverage Diff              @@
##               main    #1215      +/-   ##
============================================
- Coverage     74.69%   74.65%   -0.05%     
- Complexity     4066     4070       +4     
============================================
  Files           436      437       +1     
  Lines         12835    12861      +26     
  Branches       1301     1301              
============================================
+ Hits           9587     9601      +14     
- Misses         2484     2496      +12     
  Partials        764      764              

Files	Coverage Δ
...k/element/container/SingleBlockElementContainer.kt	43.85% <100.00%> (+2.04%)	:arrow_up:
...rc/main/java/com/slack/api/model/block/Blocks.java	89.47% <ø> (ø)
...m/slack/api/model/block/element/BlockElements.java	93.75% <0.00%> (-3.03%)	:arrow_down:
...m/slack/api/util/json/GsonBlockElementFactory.java	72.09% <0.00%> (-1.72%)	:arrow_down:
...ck/element/container/MultiBlockElementContainer.kt	75.43% <0.00%> (-2.75%)	:arrow_down:
...nsion/block/element/RichTextInputElementBuilder.kt	65.00% <65.00%> (ø)

... and 1 file with indirect coverage changes

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