rename `get_locale` selector to `select_locale`

[rekt-hard]

Note: I would really rename invenio_i18n.selectors.get_locale to select_locale, since this might avoid the confusion.

_Originally posted by @slint in https://github.com/inveniosoftware/invenio-i18n/pull/121#discussion_r1246509685_

Also need to checkout other modules which are using this selector

[chriz-uniba]

Does anything speak against this? @rekt-hard @zzacharo @ntarocco

[zzacharo]

Discussed during InvenioRDM workshop 2024:

• Deprecate the method get_locale
• Add a method set_locale and gradually iterate through every package and start using the new method.
• Once all packages have been migrated, then we can remove the deprecated method