refactored PUT /api/vaults/{v}/access-tokens/{u} → POST /api/vaults/{v}/access-tokens

[overheadhunter]

The new API accepts multiple access grants in a single requests, making bulk requests easier, as can be seen here:

hub/frontend/src/components/GrantPermissionDialog.vue

Lines 127 to 135 in 1c2133d

	let tokens: AccessGrant[] = [];
	for (const user of users) {
	if (user.publicKey) { // some users might not have set up their key pair, so we can't share secrets with them yet
	const publicKey = base64.parse(user.publicKey);
	const jwe = await props.vaultKeys.encryptForUser(publicKey);
	tokens.push({ userId: user.id, token: jwe });
	}
	}
	await backend.vaults.grantAccess(props.vault.id, ...tokens);

[SailReal]

LGTM; As discussed, we should add in the future an HTTP status code 207 like in WebDAV but we can enhance that later.