Adjustable (increased) character limit for alt text

[SleepyCatten]

Pitch

Glitch has an adjustable character limit for posts, but the limit for alt text seems to be baked in at 1,500 characters. Whilst this might sound like a lot, it actually often isn't enough to provide a full transcription for audio or for the text on images, which is an accessibility issue. I've had to break up images or audio clips into several ones sometimes in order to be able to provide full descriptive text. It is only 50% higher than the very restrictive alt text limit on Twitter and seems to be rather arbitrary, rather than something required.

Motivation

It will help with accessibility, as it will make it possible to describe images with text in full. It will also further set glitch-soc from Mastodon, which has refused to address the character or alt text limits here:
mastodon#24147

[Ember-ruby]

as an addition, only two values need to be changed

mastodon/app/javascript/flavours/glitch/features/ui/components/focal_point_modal.jsx

Line 378 in 2a34c9a

<CharacterCounter max={1500} text={detecting ? '' : description} />

mastodon/app/models/media_attachment.rb

Line 40 in 2a34c9a

MAX_DESCRIPTION_LENGTH = 1_500

an environment variable could probably be implemented like for toot chars

mastodon/app/javascript/flavours/glitch/features/compose/containers/compose_form_container.js

Line 76 in 60c2310

maxChars: state.getIn(['server', 'server', 'configuration', 'statuses', 'max_characters'], 500),

mastodon/app/javascript/flavours/glitch/features/compose/components/compose_form.jsx

Line 329 in 2a34c9a

<CharacterCounter max={maxChars} text={this.getFulltextForCharacterCounting()} />