Slackblocks

Change Summary
- Adds `InputBlock` block type: https://github.com/nicklambourne/slackblocks/pull/37

Fixes: https://github.com/nicklambourne/slackblocks/issues/31

Change List:
- Corrects out of date validation for `SectionBlock`, allowing `None` as a valid option for `text` when `fields` is provided.
- Adds a test for that use case, as well as several others related to the new validation.
- Shifts the `test_block` tests to using the new `fetch_sample` utility instead of `reads`.
- Bumps version to `v0.9.7`.

Breaking Changes:
- None

Implements remaining object/element/block classes as per API at 13 Jun 23.

The following features are now supported:
python
Attachments
Attachment,
Color,
Field

Blocks
ActionsBlock,
ContextBlock,
DividerBlock,
FileBlock,
HeaderBlock,
ImageBlock,
SectionBlock,

Elements
Button,
ChannelMultiSelectMenu,
ChannelSelectMenu,
CheckboxGroup,
ConversationMultiSelectMenu,
ConversationSelectMenu,
DatePicker,
DateTimePicker,
Element,
EmailInput,
ExternalMultiSelectMenu,
ExternalSelectMenu,
Image,
NumberInput,
OverflowMenu,
PlainTextInput,
RadioButtonGroup,
StaticMultiSelectMenu,
StaticSelectMenu,
TimePicker,
URLInput,
UserMultiSelectMenu,
UserSelectMenu,
WorkflowButton,

Messages
Message,
MessageResponse,

Views
HomeTabView,
ModalView,
View


Fixes the following issues:
- https://github.com/nicklambourne/slackblocks/issues/29 (error with calling `Text.to_text` on `Text` objects)
- https://github.com/nicklambourne/slackblocks/issues/25 (checkbox support)

Change Summary
- Moves from `setup.py` to `pyproject.toml`
- Moves from TravisCI to GitHub Actions for CI testing and publishing
- Now tests on all Python versions from 3.7 to 3.11 on both Ubuntu and MacOs
- Moves from flake8 to Black for formatting
- Differentiates between unit (always run) and integration testing (run on demand)
- Bumps version to `v0.3.1`
- Includes palewire's changes making the text input to the `SectionBlock` options.