Schema for locales_source context column should be altered

Problem/Motivation

I was trying to export the config translation to a .po files, but it turned out that i's not possible for
more complex configurations. The context column is only a VARCHAR(255), so it's not possible
to store very long contexts over there, like:
"bootstrap_barrio.settings:bootstrap_barrio_library:bootstrap_barrio_sidebar_position:bootstrap_barrio_navbar_toggle:bootstrap_barrio_navbar_container:bootstrap_barrio_navbar_top_color:bootstrap_barrio_navbar_top_background:bootstrap_barrio_navbar_color"

or
"webform.settings:settings:default_form_open_message:default_form_close_message:default_form_exception_message:default_submit_button_label:default_reset_button_label:default_delete_button_label:default_form_confidential_message:default_form_access_denied_message:default_form_required_label:default_wizard_prev_button_label:default_wizard_next_button_label:default_wizard_start_label:default_wizard_confirmation_label:default_wizard_toggle_show_label:default_wizard_toggle_hide_label:default_preview_next_button_label:default_preview_prev_button_label:default_preview_label:default_preview_title:default_preview_message:default_draft_button_label:default_draft_saved_message:default_draft_loaded_message:default_draft_pending_single_message:default_draft_pending_multiple_message:default_confirmation_message"

Steps to reproduce

Install webform or bootstrap bario theme - something that has a very complex configuration structure.
Try to export the translations.
The DB error is produced.

Proposed resolution

In my opinion, the best of what we could do is to change it to a long text, but it should be taken into consideration that this column is indexed.

Remaining tasks

User interface changes

API changes

Data model changes