Adds General option to the webhooks settings

[Godmartinz]

Description

adding a general option for webhooks, we don't test integrations on this, but it allows users to add fields if they did work before the slack validation was added. renames most variables and translation strings to webhook instead of slack (naturally).

General Option:

Slack Option:

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• [ X] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Test Configuration:

• PHP version:
• MySQL version
• Webserver version
• OS version

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

• Added a new variable called $integration_app to the SlackSettingsForm.php file
• Changed all instances of 'Slack' in the slack-settings-form blade template and lang files to use this new variable instead
• Created an array with key value pairs for different integration options, which are then used as selectable options on the form (currently only has one option)
• Updated some other variables that were hardcoded or not being set correctly

[snipe]

Can we fix the alignment and spacing with that top dropdown button?

[Godmartinz]

Changes applied and pictures have been updated.