Add Salesforce Blue colour for Salesforce Apex

[davidsbond]

Currently, Apex doesn't have a colour. It should use the Salesforce blue

[Alhadis]

@davidsbond The colour is (currently) too close to those of other languages, which is causing the colour proximity test to fail.

Hold off on attempting a fix, however. It's possible (🤞) that the GitHub team will drop the colour difference requirement now that language bars have dividers to separate colours. @lildude is currently waiting on feedback from the rest of the team, so if all goes well, we can use the official Salesforce blue instead of a compromise.

[stale]

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[Alhadis]

@davidsbond I'll make a note to update Salesforce's colour should GitHub's colour-proximity restriction be lifted in future. 👍